Semen quality was evaluated in 256 men at 2, 4, 6, and 12 months after vasectomy reversal. Total sperm counts were normal and averaged 91 X 10(6) sperm per ejaculate. The percentage of live sperm was decreased below normal to 36% and hypo-osmolarity values indicated only 41% of the sperm with normal membranes. Progressive motility and the total progressively motile sperm count were reduced and averaged 25% and 27 million, respectively. Approximately 50% of the patients had positive titers of sperm agglutinating and/or sperm immobilizing antibodies. Sperm morphology indicated tail and head shape defects with increases in both tapered and immature sperm. A fertility score combining several sperm parameters averaged only 37% of normal. All of these values remained constant with time after reversal except for progressive motility (increased), oval head shapes (increased), and tapered sperm (decreased). This study has demonstrated that characteristic defects occur in sperm (decreased). This study has demonstrated that characteristic defects occur in sperm motility, sperm membrane function and morphology, in addition to specimen fertility scores, after a vasectomy reversal and need to be taken into consideration when advising and treating these patients for subsequent fertility difficulties.