1. The serum profiles of chlorpropamide obtained following single doses of two tablet preparations and from a suspension formulation have been compared in healthy volunteers. The amounts of chlorpropamide absorbed from the three formulations were similar but the drug was absorbed more rapidly from the suspension than from either tablet formulation. There was a small but therapeutically insignificant difference in the rate of absorption of the drug from the two tablets. 2. Changes in blood glucose concentrations were found to be related to the drug serum profile characteristics of the formulations.