Biochemical analysis of semen was performed in six men with bilateral macro-orchidism. It has been shown that marker levels of the seminal vesicle secretion (fructose) are higher, whereas marker levels of prostatic secretion (citric acid and calcium) are lower, in these men than in those of a control group of normal men. Whether the pathogenesis of these findings was due to a benign enlargement of the accessory sex glands or not remains to be elucidated.