Background: Sperm functional tests as an addition to semen analysis have been used to study the fertilization ability of spermatozoa. Besides the usual variability of the seminal analysis an individual variability in the results of functional tests has been recently found. Aim: to evaluate in a three months period, the individual variability of sperm parameters and sperm maturation using the chromatin condensation test and epidydime alpha-glucosidase (that allows to discriminate obstructive processes). Material and method: The evaluation was carried out in two donors (12 samples) apparently in good health. One of them presented evident semen analysis alterations (donor 1) and the other was considered normal under the WHO standards (donor 2). Results: The averages for donor 1 were: Sperm count 24x106 sperm/ml (range 10-58x106 sperm/ml), morphology 31.8% (range 30-35%), total motility 33% (range 20-42%), sperm maturation 38% (range 28-78%), a-glucosidase 8.65 (U/ml (range 5-10 (U/ml). The averages for donor 2 were: Sperm count 96x106 sperm/ml (range 50-140x106 sperm/ml), morphology 32.2% (range 30-35%), total motility 69% (range 58-78%), sperm maturation 17% (range 7-30%), a-glucosidase 36.9 (U/ml (range 20-82 (U/ml). Conclusions: These results show that significant variations can be found in the sperm parameters and in seminal plasma a-glucosidase; however these variations are generally maintained at the normal or abnormal ranges for each individual, except the sperm morphology that was constant and with low variation in both donors. The determination of the chromatin condensation in the semen analysis gives an additional information about the grade of sperm maturation and would be of great value for differentiating between sperm samples that show similar morphology values. (Rev Méd Chile 2000; 128: 483-9)