The aim of the study was to determine the semen parameters of a proven fertile population and to compare these parameters with that of a subfertile group in the same region. Sixty-nine fertile male patients were studied and compared with 93 patients recruited at an infertility clinic. A sub-sample of patients was matched according to age. Sixty-one were studied in the fertile group and 62 in the infertile group. Receiver operator characteristics analysis was done on the sub-sample. The threshold value of the progressive motility was 42% and it was the best parameter with sperm morphology to distinguish between the two groups. At 69% sensitivity and 67% specificity the sperm morphology threshold was 12% normal forms. If the positive and negative predictive value was used to screen the general population to identify the subfertile group, a 5% normal morphology threshold was indicated with 14% progressive motility, 30% motility and a concentration of 9x10(6)/ml or lower. The negative predictive values of the parameters were good and achieved 90% in most cases. The sensitivity of the semen parameters at the reported thresholds was poor and indicated a large overlap in the distributions of these variables in the fertile and infertile groups. To distinguish between the fertile and subfertile population, the most significant finding of this study was the progressive motility with a threshold level of 14%. The cut-off value of the sperm morphology (5%) in vivo was consistent with the previous publications in assisted reproduction programmes for sperm morphology.