Split samples of boar semen were frozen when (a) sprinkled in liquid nitrogen, (b) placed in a glass tube and dropped into liquid nitrogen and (c) pelletted on dry ice. One hour frozen (a, b, c) samples and the control, a split sample of fresh semen (d), were fixed and used for electron microscopy. Qualitatively, the effect of freezing was so drastic to all the three treatments that even the nuclear membrane and perforatorium were damaged. Plasma membranes of almost all the treated cells were denuded. In more than 80% of the cells, the outer acrosomal membrane (OAM) was undulated or broken and the acrosomal vesicles (AV) showed localized or generalized vacuolations. These parameters were considered as a typical response or the acrosome against any method of quick freezing. A total of 3,299 cells, randomly distributed in the photomicrographic plates in sagittal, cross or oblique sections, was examined. In sagittal and cross sections of fresh semen the OAM were 81% smooth; and the AV showed 87% normal. However, due to rapid freezing the values of the OAM changed to 5-8% smooth, 66-76% undulated and 17-27% broken; and similarly the AV showed 7-15% normal, 60-72% localized and 22-25% generalized vacuoles. Further in the control sample-oblique sections, the OAM were 85% smooth and the AV were 83% normal. While after freeze-shock treatments the OAM were 3-6% smooth and 94-97% undulated or broken, Similarly, the values for AV were 14-36% normal and 64-86% vacuolated. Because of a very high incidence of the typical responses of accrosomes, the parametric evaluation of any of its two characters-e.g. alterations in the OAM or in the AV could be used as an index for evaluating freezability of boar spermatozoa.