Troglitazone is a novel once-daily oral antidiabetic agent for the treatment of type 2 diabetes patients. Here, we report the overall dose response characteristics of troglitazone, with respect to effects on metabolic control, using a pharmacodynamic model. Data from week 12 from two previously reported double-blind, randomized, parallel-group, placebo-controlled, dose-ranging multicentre studies examining once-daily doses of 10, 30, 100, 200, 400, 600 and 800 mg of troglitazone were combined for the analyses. The pharmacodynamic relationships for relevant parameters of metabolic control were modelled using a nonlinear regression modelling programme. The troglitazone dose-concentration relationship was linear over 10-800 mg. Using an inhibitory sigmoid Emax model, ED50 values of approximately 100 mg and 200 mg were found for fasting serum glucose and triglycerides, respectively. The 200 mg dose for HbA1c showed an inconsistent reduction compared with placebo between the two studies; this illustrates the difficulties associated with comparing results from different assay techniques. Insulin and nonesterified fatty acid reductions compared with placebo were not consistent between studies, and no pharmacodynamic modelling was possible. No changes in body weight were observed at any dose. Troglitazone was as well tolerated as placebo across the dose range investigated. This pharmacodynamic analysis has established that 200-600 mg once daily can be considered the therapeutic dose range of troglitazone that significantly improves metabolic control in type 2 diabetes patients.