This study was designed to determine any correlation between infertility and semen quality with concentrations of total carnitine in human seminal plasma. Seminal plasma total carnitine concentrations were determined in 79 men. The seminal plasma of 65 infertile men and 14 men as a control group with proved fertility were investigated. The concentrations of total carnitine were reduced significantly in the infertile group compared to the control group (31.52 +/- 20.77 vs. 45.52 +/- 10.73 mg/l, P<0.05). The 65 infertile men were divided into five groups according to their sperm analysis: normospermia (n=42), oligospermia (n=23), asthenospermia (n=40), teratospermia (n=44) and oligoasthenospermia (n=10). Total seminal plasma carnitine concentration differed significantly between controls and the patient groups (P<0.05). There was a statistically significant positive correlation between seminal plasma total carnitine concentration with total sperm count and the percentage of normal forms (P<0.05 and P<0.01, respectively). Total carnitine concentration was found to be low in the asthenospermia group when compared with the group of patients, whose total motile sperm percentage was 51 (P<0.05). These findings suggest that the determination of seminal carnitine levels may be a useful test in evaluation of male infertility.