The testicular sizes of 305 men were measured by a recently developed orchidometer and related to 9 other known parameters of testicular function. Mean testicular size had the strongest correlation with serum follicle-stimulating hormone levels, total sperm count and sperm concentration, while a significant correlation also was noted with sperm motility, percentage of live sperm, sperm morphology (normal and immature forms), and serum luteinizing hormone and testosterone levels. Sperm quantity had stronger correlations with testicular size than did sperm quality, although both were impaired in testes smaller than 14 ml. It is concluded that the size of the testis bears a direct correlation with testicular function and, thus, it can be helpful to assess rapidly andrological status during the initial physical examination.