In this study were collected 34 normal semen samples, and samples from 8 men showing prostatic hypofunction of unknown origin and from 5 men with agglutinating autoantibodies in their sera. Among the various biological solutions tested, Tyrode's solution, with or without glucose, bovine serum albumin, and sperm-Ringer solution containing fructose best maintained the motility of normal spermatozoa, which was nearly the same as with semen samples. The ATP content of the spermatozoa was highest in the Tyrode's solution. When seminal plasma of the samples with low acid phosphatase and poor sperm motility was replaced with normal donor seminal plasma, the motility was increased almost to the normal level. All other biological solutions tested were weaker in this respect. 7.2 mmol/l caffeine had neither clear improvement on the motility of normally motile sperm cells nor on the spermatozoal ATP content. After cryopreservation and thawing, the samples containing caffeine showed the best motility, which was, however, surprisingly low. Spermatozoa coated by autoantibodies showed very abnormal cervical mucus penetration. After washing with Tyrode's solution the penetration improved, but did not reach normal penetration level.