Control extender was incubated at 4 degrees C for 24 hours. Rubber or plastic syringe plungers were separately incubated in semen extender for 24 hours at 4 degrees C. Following incubation, the extender was stored at -20 degrees C until the time of semen collection. The treatments consisted of the following: Group A = equine semen plus control extender; Group B=equine semen plus extender incubated with rubber plungers and Group C=equine semen plus extender incubated in plastic plungers; Group D=equine semen plus control extended in rubber plunger syringes and Group E=equine semen plus control extender in plastic plunger syringer. Each group contained a 5-ml volume of semen and extender at a concentration of 1.0 x 10(8) sperm/ml. The number of live spermatozoa, percentage of progressively motile spermatozoa and rate of progressive motility were taken following collection and every 15 minutes for 1 hour following application of treatments. In experiment 2, treatments were allowed to incubate with semen for 45 minutes, then the extender was removed and was replaced with fresh extender. The rate of progressive motility and the percentage of progressively motile spermatozoa were taken immediately, at 45 minutes, and then every 15 minutes for 1 hour. In experiment 1, the number of live spermatozoa was not affected among the 5 groups. However, there was a decrease (P<0.01) in the rate of progressive motility and in the percentage of progressively motile spermatozoa in Group B compared with the remaining 4 treatment groups at 30, 45 and 60 minutes, with no differences noted when semen was held in syringes with a rubber or a plastic plunger. In experiment 2, the percentage of progressively motile spermatozoa increased after the addition of the control extender.