The concentration of spermatozoa in human semen has been assessed by counting in the microscope with a hemocytometer and by counting with the Coulter Counter ZF. The Coulter Counter was supplied with a 100‐channel pulseheight analyzer, Channelyzer C‐1000, and a tape‐punch for further handling of data in a desk‐computer. It was found that the number of spermatozoa (less than 106per ml) was over‐estimated with the Coulter Counter. By subtraction of the non‐spermatozoan background with the aid of mathematical curve‐fitting procedures, these values could be corrected. To allow such an adequate analysis without the use of pulse‐height analyzer and computer, the background corrections were simulated for the relative number of counts obtained at specified settings of the threshold levels (T) and other variables on the Cou