One hundred and twenty-eight samples of human semen, divided into four groups according to sperm counts, were fractionated on two types of columns of discontinuous gradients of bovine serum albumin (3%, 15%, or 7.5%, 17.5%). In addition to morphology and motility, protein and DNA contents of spermatozoa as well as microscopical pictures of their sediments were examined in order to assess sperm sensitivity to damage in the course of common isolation procedures. The proportions of morphological normalcy and motility grades within the groups were higher in the bottom column fractions than in the middle ones; both showing prevalence over parent semen. Motility percentages were also higher in the bottom than in middle fractions, but no prevalence over parent semen was observed. Protein and DNA contents of spermatozoa were similar in the two fractions within the same group. Comparison between groups revealed an increase in percentages of normal morphology and motility and a decrease in protein and DNA with elevation of sperm density. Microscopic examinations revealed similar degrees of contamination in both fractions which were more abundant in oligospermia than in normospermia. It is suggested that sperms with better morphology and motility are as sensitive to common laboratory procedures as cells of lower quality originating from the same specimen.