Estimation of protein biosynthesis rate was used for rapid determination of Vibrio cholerae sensitivity to tetracycline and chloramphenicol by comparison of the bacterial cell radioactivity in samples with and without the antibiotics. For the sensitivity determination the strains were grown for 30 minutes at a temperature of 37 degrees C in nutrient media with a 14C-amino acid and antibiotic. The data of the determination were indicative of at least 10-fold difference in the amount of the amino acid assimilated by the sensitive strains in the presence and absence of the antibiotic. The value of the label incorporation into the antibiotic resistant strains under the above conditions did not differ. Complete coincidence of the results obtained upon parallel testing of the strain antibiotic sensitivity by the rapid and routine methods was observed.