There have been attempts to select the sex of a child prior to conception in both animals and humans. Centrifugation, microelectrophoresis and density gradient sedimentation have been used to separate X and Y sperm in animals. Only the latter technic has produced a change in sex ratio. In the human, timing of coitus or artificial insemination in relation to ovulation has been the popular method for influencing the sex of a child. This review suggests caution in accepting the claims of success for coital timing. Sperm bearing the Y chromosome can now be identified by quinacrine staining. Using this marker, Ericsson showed that when sperm are allowed to swin into columns of liquid albumin a high percentage of Y-bearing sperm are found in the most distal portion of the column. At this time it has not been shown whether the fraction enriched with Y sperm can produce a preponderance of males.