In this work, we have compared two procedures that evaluate the acrosomal status of human sperm bound to the human zona pellucida. Motile sperm, selected by a Percoll gradient, were capacitated by incubation at 37°C, 5% CO 2, for 4.5 h, at 20 × 106 cells ml-1. Then, the sperm were incubated with nonviable human oocytes for 10 min at 37°C, 5% CO2. The oocytes with bound sperm were transferred to 500 μl phosphate-buffered saline (PBS) and washed to remove loosely bound sperm. The oocytes were then processed according to the procedures of Cross et al. (1986) or Liu & Baker (1996). In the Cross's procedure, the sperm were labelled while they were bound to the zona. In the Liu's procedure, the sperm were first dislodged from the zona into a droplet of PBS and labelled in there. Both procedures gave equivalent percentages of acrosome-reacted sperm. However, the total number of zona-bound sperm available for assessment with the procedure of Liu & Baker was greater than that of Cross et al. We suggest to use the former procedure to evaluate the acrosomal status of zona-bound sperm in humans. Moreover, this procedure also provided information about sperm ability to bind to the zona pellucida.