Read this article....

There are some other options, but they have advantages and disadvantages. If you would tell us why you don't wish to use ONPG and what the problem is, you might be able to get better suggestions.

@Michael J.Benedik

I want to mesure by colorimetric methods my bacteria enzyme activities. The only problem that I have with onpg is that it is not disponible in our lab. Only have some onpg disks and I don't know their concentration with ONPG.

That is why I am searching for another product that substitute it might be disponible.

Very wierd problem. Try to purchase or borrow some ONPG from a colleague.

I think ONPG is the most readily available substrate and easiest to assay. The other substrates are likely to be harder to obtain and some, such as the fluorescent substrates, require more complicated instrumentation to measure. Perhaps another lab at your institution is set up to run the assays and has some available.

4-methylumbelliferyl β-D-galactopyranoside (MUG) is a fluorescent reporter. But buying this will probably be costlier than ONPG. Personally, I also recommend ONPG.

Chapter Measuring β-Galactosidase Activity in Gram-Positive Bacteria...