It depends where you are and what you want to do with them. 70% ethanol is more usual than 100%. Formaldehyde and then 70% ethanol is better still for tissue preservation, but is not realistic in field conditions. For preserving cell structure, there are several fixatives that are better than formaldehyde. If you want to keep samples for later extraction of DNA, and cannot use freezing, then the link below takes you to a useful paper.

http://www.nrcresearchpress.com/doi/abs/10.1139/z91-013#.U1b1I_ldXfA

Yes, the samples will be collected in the field ( the weather will be hot). The samples are for later extraction and I need high quality DNA, hence my concern.

Thank you very much, you answer was really helpfull I will check the bibliography that you indicated!

Telma ... that paper will be very helpful for you. I've attached it here in case you have difficulty downloading it..

Telma ... by the way, make sure you learn how to handle the chemicals safely. DMSO passes through human skin readily, so you should not get it on your hands.

Martin Willison, I have already worked with DMSO and I am alert regarding the safety issues, I will try to avoid the use of anything other than ethanol in the field and always wear gloves. Thank you again!

Vaithianathan, thank you for your reply but unfortunately that method is not a option to me. Thank you for answering!

Telma and Martin, while preserving the tissue in Ethanol, have u come across any information on using chemicals to disintegrate the tissue?

Like after the sample is collected, and transfered into ethanol containing tube if I want to use some chemical ingredient within the ethanol which will disintegrate the tissue (during shipping 2-5 days)  which chemical can be used ? Have u come across any such information.?

And after it reaches the destination we would isolate DNA/RNA, so the chemical which we wish to add into the ethanol should not effect the purity of DNA/RNA.

well I believe that the digestion of the tissues should always be performed on the lab already in controlled environment at right temperatures... proteinases usually require specific temperatures to be activated and digest the tissue without affecting the DNA. But I'm not sure if there are other alternatives... but doind this in the lab would only take you around 3 hours more... so if time is your question I don't think it compensates to jeopardize your samples during transportation, i feel it's too big of a risk... but lets see if someone else knows about other methodologies

I have preserved helminth parasites in 70 percent ethanol how long they will remain so that I can extract DNA

I think that éthanol 70% is more useful for biological tissues.

70% ethanol; Nick E

70-75% etOH for morphological purposes chiefly museum specimens, but can be good enough for DNA sequencing. Use 100% etOH solely for molecular purposes.

Here we store our ground geetles (Carabidae) in Scherpeltz-liquid (70% ethanol, 25% water, 5 % acetic acid).