We have investigated the accuracy of protein synthesis in somatic tissue of young and senescent Drosophila melanogaster by means of two-dimensional electrophoresis. Electrophoretic heterogeneity characteristic of translational error could not be detected at either age, placing the error frequency below about 4 X 10(-4) per codon. As a positive control on the efficacy of the technique, we showed that electrophoretic heterogeneity is detectable in bacterial cells grown in streptomycin, and that the error frequency calculated from these data is in good agreement with independent measurements. Such cells can tolerate an error frequency of about 3 x 10(-3) without cell lethality, or error catastrophe. Since the Drosophila somatic error frequency is at least eight times lower, even in senescent organisms, translational error is unlikely to be a cause of senescence in Drosophila.