We routinely freeze cell pellets in Trizol at -70 for extended periods of time with no noticeable differences in RNA yield compared with fresh samples. From the Trizol protocol: "Homogenized samples can be stored at room temperature for several hours, or at –60 to –70°C for at least one month."

http://tools.lifetechnologies.com/content/sfs/manuals/trizol_reagent.pdf

You can freeze your pellets like that. If you have some problems to the disrupt the pellets, you could use some ceramic beads.

I haven't tested this approach but it is generally not advisable. 3-4 days is OK but it is not exactly perfect for storing RNA for longer periods of time because TRIzol is said to degrade with time. The perfect solution for proper pre-isolation archiving of your cells or tissues is RNALater http://www.lifetechnologies.com/pl/en/home/brands/product-brand/rnalater.html

We routinely freeze cell pellets in Trizol at -70 for extended periods of time with no noticeable differences in RNA yield compared with fresh samples. From the Trizol protocol: "Homogenized samples can be stored at room temperature for several hours, or at –60 to –70°C for at least one month."

http://tools.lifetechnologies.com/content/sfs/manuals/trizol_reagent.pdf

Thank you for all the answers. I'll compare the quality of fresh and stored samples definitely.

I have stored cells and whole lung tissue in TRIzol at -80°C for almost one weak. RNA quality was good, however i shall add that i have used DEPC treated tubes and tips...

I agree with Filip. Use RNALater for long term storage. In fact, we have perfused animals with RNALater so that the RNA stability chemistry (Guanidinium thiocyanate) gets into the tissues prior to freezing and storage. However, if the TRIzol storage works, just keep doing it.

It's really interesting - thank you Jamiee for link to protocol. Mine (for TRIzol Plus RNA Purification) lacks this note about storage of homogenate. I've asked the life technologies support the same question and they replied that storage in TRIzol reagent is not advisable which is a bit confusing

I agree with Jaimee Hoefert. It is a routine practice for RNA extraction when you want to store the biomass and use it later. Nothing is wrong.

I've checked it myself and now I can confirm that RNA isolation from previously frozen homogenate in TRIzol gives RNA of high concentration, purity and quality. Thank you again for all answers.

RNAlater is okay to use so long as you don't plan to do an organic extraction (trizol/phenol-chloroform) followed by column purification, as the OP indicated.  I have had great success using Trizol and storing at -80C for several months.  I have done both suspension cells and adherent cells (make sure to neutralize trypsin), and I have done both pelleting of cells first or direct homogenization from the culture flask/plate.  Just make sure to work quickly, homogenize well, and freeze promptly (follow Trizol documentation for correct volumes, etc.).  In fact, I prefer to do it this way because it adds a freeze-thaw step.  RNAlater is better used for tissues rather than cultured cells, and if you plan organic extraction, you have to make sure to remove all RNAlater beforehand.  Best of luck to you!

@ Katarzyna Dziedzic.. How old frozen samples have you tried?

As far as I remember up to 3 months.

Canany one help me .. I kept my tissues in Trizol without homogenized in -20 .. if I do RNA extraction could I get good RNA quality?

Asma Sunker, I'm not sure freezing unhomogenized tissue in TRIzol is good. Also always when you want to isolate RNA out of tissue or cells you must place the sample for the storage in -80C. RNA degrades in higher temperatures.

Dear Asma

Do not go by "ifs and buts". Just try it out. If your freezing of the has unhomogenized tissue samples been rapid with minimum loss of moisture, then there is no doubt that you might get good RNA isolated. It all depends how you have frozen it. However, if the freezing was slow then by the time you thaw it, the cells in the tissue would have laked out and you won't get anything.