In this study, the serum total, free and ester carnitine levels in 24 type II diabetes mellitus (DM) patients with complications and 15 type II DM patients with no complications were investigated. The patients were investigated in four groups; the control group included the patients with no complications (group 1), the groups including the patients with retinopathy (group 2), hyperlipidemia (group 3), and neuropathy (group 4). In addition, patients were grouped into two. The first group included 10 patients who took insulin by injection (group 5), and the second group included 29 patients using antidiabetic drugs orally (OAD) (group 6). Free and ester carnitine levels were determined by using Boehringer Manheim UV-enzymatic L-carnitine kit. Statistical analysis results showed that both the plasma total and free carnitine levels of groups 5 3, and 4 were found to be low when compared to the levels of group 1 (p < 0.05). It was observed that the plasma total and free carnitine levels of group 5 were lower when compared to group 6. No significant difference was observed between the plasma ester carnitine levels of all the groups investigated. As a result of this study, it has been thought that carnitine plays an important role in diabetes mellitus complications. (C) 2000 Elsevier Science Inc.