An attempt was made to compare different pre-treatment techniques in 16 normal and proven fertile and 30 subnormal and hitherto infertile semen samples. The techniques used were (i) standard, (ii) layering, (iii) discontinuous Percoll density gradient and (iv) albumin columns. Percoll gradient was most effective in separating a high fraction of progressive motile spermatozoa (75 and 57% in normal and subnormal semen samples, respectively). The albumin columns, as well as the standard techniques, were equally effective in recovering 45 and 24% respectively of progressive motile spermatozoa in normal and subnormal semen samples. The layering method was the least effective of the four techniques (4% recovery in normal and subnormal semen samples). In cases of contamination with inflammatory cells, the standard and layering methods were significantly (P less than 0.001) more advantageous than isolations with Percoll gradient and albumin columns. The percentage of ideal forms of spermatozoa recovered from a normal semen sample was significantly higher with the standard (P less than 0.01), layering (P less than 0.05) and Percoll gradient (P less than 0.05) techniques. In subnormal samples, only the Percoll gradient gave a significantly (P less than 0.02) higher percentage of ideal forms, whereas the other techniques were less effective. The significance and practical use of the various pre-treatment techniques are discussed in relation to the characteristics of the pre-treatment semen sample.