The disappearance of spermatozoa from the ejaculate after vasectomy is said to be influenced by age, frequency of ejaculation, and time since operation. Since their relative importance is not clear the authors examined the histories of 624 men who underwent vasectomy at the Margaret Pyke Centre from July 1971 to October 1972 to investigate the independent effects of these factors on the clearance of spermatozoa. These results suggest that age and coital frequency have a complex relationship t...