The possible effects of varicocele and of the varicocelectomy procedure on Sertoli cell function were investigated. Transferrin concentrations in seminal plasma in men with varicocele before and 3 months after the operation were evaluated. Concentrations were measured in 10 normozoospermic fertile men as a control group and 32 oligozoospermic men with varicocele. Also, sperm analysis before and 3 months after the operation was performed. The mean transferrin level in seminal plasma was 108.4+/-17.5 mu g ml(-1) in normoozoospermic men and 58.1+/-14.4 mu g ml(-1) in patients with varicocele before the operation (P<0.0001). Mean sperm concentration, motility and normal morphology ratio showed significant improvement 3 months after the operation (P<0.0001). Although the mean transferrin level increased slightly (to 60.8 +/- 16.2 mu g ml(-1); P=0.2), there was a statistically significant correlation. between the change in transferrin concentration and the change in sperm concentration after the operation (r=0.56, P=0.0008). These results showed that elevated transferrin secretion after the treatment seems to be associated with an increase in sperm concentration after varicocelectomy. The finding of improvements in seminal parameters after the operation but insignificant changes in seminal transferrin levels indicates that varicocelectomy results in a greater improvement in sperm quality than in Sertoli cell function.