This randomised, double-blind, parallel-group study assessed the effects of addition of the dual peroxisome proliferator-activated receptor (PPAR) alpha/gamma agonist, tesaglitazar, for 24 weeks to the therapeutic regimen of 392 poorly controlled (glycosylated haemoglobin [HbA1C] 7.5-10%) insulin-treated, type 2 diabetes patients. At 24 weeks, tesaglitazar 0.5 mg resulted in a 0.66% (95% confidence intervals: -0.85, -0.47; p<0.0001) reduction from baseline in HbA1C, and reduced fasting plasma glucose (p<0.0001) and daily insulin dose (p=0.014) versus placebo. After 24 weeks, tesaglitazar caused greater improvements from baseline in triglycerides (p<0.0001), high-density lipoprotein cholesterol (HDL-C) (p<0.001), non-HDL-C (p<0.05), apolipoprotein (apo)A-I (p<0.05) and apoB levels (p<0.01) than placebo. Tesaglitazar was generally well tolerated but was associated with a greater increase in serum creatinine level than placebo. The clinical development of tesaglitazar is no longer continuing; its effects on the glucose and lipid abnormalities of type 2 diabetes suggest that the concept of dual PPARalpha/gamma agonism is worthy of further investigation.