The bioavailability of three lots of a generic 200-mg carbamazepine tablet, which had been withdrawn from the market, was compared to the bioavailability of one lot of the innovator product in 24 healthy volunteers. Fifty-three lots of the generic product had been recalled by the manufacturer because of concerns over reports of clinical failures for several of the lots. The three generic lots tested in this study exhibited a wide range of bioavailability, as well as large differences in the in vitro dissolution rates. The mean maximum carbamazepine plasma concentrations for two of the generic lots were only 61-74% that of the innovator product, while the third lot was 142% of the innovator. The mean areas under the plasma concentration-time curve for the three generic lots ranged from 60 to 113% that of the innovator product. The results clearly indicate a significant difference in the rate and extent of absorption of the generic products compared to the innovator, as well as among the generic lots. A good relationship was found between the in vivo parameters and the in vitro dissolution results for the four dosage forms.