A method is developed to improve the quality and the number of sperm recovered after laboratory processing, consisting of a swim-down technique. This study was designed to compare quality sperm after selection with a swim-up and a swim-down method. Fifty-nine men, 23-52 years of age, with a period of infertility of 1 to 14 years were included in the study. The efficacy of the swim-down technique as compared to the swim-up technique was assessed by measuring percentage of sperm recovery, sperm motility, the hypoosmotic swelling test, acrosome reaction, and the sperm penetration to zona-free hamster oocyte assay. The swim-down procedure using pure serum as culture medium showed a higher percentage (p < 02) of spermatozoa with forward progression and a higher number of recovered (p < 05) spermatozoa than the swim-up technique. The fertilizability was similar with both methods. The swim-down procedure using pure serum could be useful for intrauterine insemination where a higher number of spermatozoa is required. © 1993 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.