Distortion products are currently considered an objective method for rapidly evaluating the functional status of the cochlea, which is interesting for the monitoring of drug ototoxicity. We studied 40 ears from patients who had received an ototoxic drug, tobramycin. Two consecutive measurements were made using distortion products 2f1-f2, before and after taking the ototoxic agent. A significant reduction was observed in the amplitudes of the DP-grams. At the same time, we evaluated the influence of previous hearing loss on the DP-grams and divided the patients into two groups: normal hearing and sensorineural hearing loss. Patients were evaluated at the same time by conventional audiometry to compare the effect of tobramycin on both tests. To conclude, tobramycin had little effect on audiometric thresholds, but produced an evident change in the amplitude of the distortion products.