The percentual change in the content of pro-acrosin taking place in ram semen preserved for a short and long time was examined in the period from April to October. Two diluents for keeping semen at the temperature of 16 degrees C and one diluent for keeping semen at 3 to 4 degrees C were used in short-time preservation. The content of pro-acrosin was measured 2, 8 and 12 hours after dilution. The lactoso-yolk diluent and the diluent after Milovanov (1980) were used for cryopreservation. The content of pro-acrosin was examined before and after semen freezing. In short-time preservation, no statistically significant decrease of pro-acrosin content was demonstrated in the H Milch diluent (Peter, 1975) at the storage temperature of 16 degrees C and in the diluent after Milovanov (1980) at the temperature of 3 to 4 degrees C. In the diluent prepared after Milovanov (1980) a significant decrease of pro-acrosin content during preservation was recorded at the storage temperature of 16 degrees C. When the short-time preservation diluents were compared, significant differences in pro-acrosin content were found between them. In the long-time preservation diluents a significant difference in pro-acrosin content was found before and after semen freezing; the difference between the short- and long-time preservation diluents was also significant. A positive correlation was found between sperm activity and pro-acrosin content.