The functional integrity of the sperm (SPTZ) membrane is believed to be an important factor in fertilization. This function was assessed by Jeyendran et al. (Journal of Reproduction and Fertility, 70: 219-228, 1984), who concluded that when SPTZ from normal fertile men are exposed to a hypo-osmotic solution with an ionic strength of 0.15 mol/l, 60% or more will exhibit tail swelling Essentially no changes have occurred in the test procedure since it was first published, except that SPTZ could be fixed after exposure to the hypo-osmotic solution and observed at a later time using a phase-contrast microscope. We describe here a simple test which does not require phase-contrast microscopy to read a stained preparation after the hypo-osmotic test. A drop of semen preincubated in the hypo-osmotic medium of Jeyendran et al. and fixed with 18.5% formalin is placed on an albumin-coated slide. A second (spreader) slide is placed on the first as a coverslip and pulled forward at moderate speed until all the sperm has been spread into a moderately thin film. The preparation is then air dried and submitted to Papanicolaou staining. The slide can be read at any time after staining with a light microscope and provides permanent documentation.