The study of mycoplasma enzymes involved in nucleotide degradation and base salvage pathways allowed determination of enzyme profiles for some species. The activity of adenosine phosphorylase seems to be the biochemical test of choice to detect mycoplasma contamination in cell cultures. All mycoplasmas tested had a very high level of activity compared to very low activity in human cell cultures, rendering the technic sensitive even at a low degree of contamination.