The examination of semen as it is generally done is quite inadequate. Usually the contents of the condom are examined for (1) semen fibers and (2) mobile semen fibers and the number of mobile semen fibers is roughly computed. Owing to the recent research by Macomber and Sanders, Mönch, Stiasny and Generales, Michael, and Joël and Pollák, the exact obstructions to fecundity in a man can be ascertained. There are three conditions to be observed in investigation of the sperm: The examination should be preceded by a pause in ejaculation of from four to seven days at least. Only one ejaculation should take place in order to provide material for examination. The material should if possible be obtained by the physician through auto-erotic manipulation or coitus interruptus. The contents of the condom are unsuitable, and other ways of obtaining material are inadequate. The material should be examined