Abstract: A stabilizer for radioactively labelled organic compounds has the general formula ##STR1## where R is C1 to C4 alkylene which may be OH substituted, m is 0 or 1 (i.e. R may be absent or present), X is carboxyl or sulphonyl e.g. COOH or SO.sub.3 H or a salt thereof and n is 1, 2 or 3. Radiolabelled compounds of biological origin, such as nucleotides and amino acids, may be stabilized either in solution or in the freeze-dried state. For example, L-[.sup.35 S]methionine may be stabilized to prevent formation of a 47 KD band in protein transcription/translation experiments.