A study of sperm head morphology in unexposed workers was conducted as part of a study of semen characteristics of unexposed workers. The study group consisted of 45 males, 25 to 35 years old, from the Cincinnati, Ohio area. They were employed in blue collar and white collar jobs that involved no known toxicant exposures. Approximately 80% drank alcohol, 52% smoked cigarettes, cigars, or a pipe, and 46% had fathered at least one child. Monthly semen samples were collected by masturbation for 9 months. The samples were analyzed by morphometric techniques that included determining sperm head area, perimeter, length, width, and the width/length ratio. The oval factor, defined as the ratio of the sperm head area to the square of its perimeter per 100 sperm cells, was computed. Tolerance intervals were calculated for individual cells and sample means for each morphometry parameter. The tolerance limits contained 75% of all coefficients of variation across all the subjects. The grand mean tolerance intervals for the sperm head morphometric variables were: length 4.53 microns, width 2.85 microns, area 8.72 square microns, perimeter 12.69 microns, width/length ratio 0.641, and oval factor 0.688. The authors conclude that the tolerance intervals provide useful information on the range of cells found in ejaculates from unexposed male workers. The largest source of variation appears to be due to cell to cell variability. This suggests that each ejaculate contains a variety of sizes and shapes of sperm heads.