Semen volume, pH, sperm characteristics and the ejaculate content of six compounds secreted by the epididymides, prostate and seminal vesicles are presented for several semen samples from 25 men (mean age 31 years) who, without clinical assistance, had fathered children within the previous 29 months. There was a large variation both within and between individual's samples for concentrations and amounts per ejaculate of all parameters except pH. The range including 96% of all values from these fertile men are presented as standards against which samples from infertile men could be compared. Lower limits (combined arithmetic means minus twice the combined within- and between-father standard deviation) were: for semen volume, 1.9 ml; for semen pH, 7.4; for total sperm count, 39 X 10(6); for normal morphological forms, 42%; for motility (WHO grades) a, 4%; b, 19%; c, 1%; d, 19%; for curvilinear velocity, 27 microns/s; for total glucosidase, 27 mU/ejaculate; for neutral alpha-glucosidase, 17 mU/ejaculate; for L-carnitine, 0.4 mumol/ejaculate; for glycerophosphocholine, 2.4 mumol/ejaculate; for fructose, 15 mumol/ejaculate; for citrate, 30 mumol/ejaculate; for zinc, 2.8 mumol/ejaculate.