Chromosome complements were studied in 118 sperm from a man heterozygous for a 15;22 Robertsonian translocation using the human sperm/hamster oocyte fusion technique. Alternate segregation occurred in most spreads (89.6%) and the proportion of normal (42.6%) and balanced complements (47%) was approximately equal. The frequency of sperm that were unbalanced with respect to the translocation was 10.4% and all categories of unbalanced sperm were observed (-15, -22, +15, +22). The frequency of chromosome abnormalities unrelated to the translocation was 7.6%. Since the frequencies of both numerical (3.4%) and structural abnormalities (3.4%) were within the normal range of control donors, there was no evidence for an interchromosomal effect. The frequencies of X-chromosome bearing (48%) and Y-chromosome bearing (52%) sperm were not significantly different from 50%. Data on this translocation were compared to the 4 other reports of cytogenetic analysis in sperm of Robertsonian translocation carriers.