The effects of electric current (in vivo and in vitro) and seminal plasma on epididymal and ejaculated sperm obtained from C57BL x CBA and C57BL/6J mice were investigated by studying motility parameters, fertilization and embryo development. Electroejaculates were obtained by applying a series of computer-generated sinusoidal alternating currents (0.25-3.0 V at 50 Hz) delivered for 1, 2 and 3 s with 1-s rest periods using a four-electrode rectal probe for 4 min. Epididymal sperm obtained from the same mice were either subjected to electric current in vitro in a Plexiglass chamber or incubated in a medium containing seminal plasma for 2 h. In vitro electric current application and incubation in a medium containing seminal plasma significantly (P < 0.01) decreased sperm motility. Neither electroejaculates nor epididymal spermatozoa incubated with seminal plasma could fertilize oocytes by conventional IVF (P < 0.001), whereas sperm subjected to in vitro electric current had lost little of their ability to fertilize oocytes. Following transfer of embryos generated by intracytoplasmic sperm injection (ICSI), the number of live pups obtained from electroejaculated sperm (10.2%; 6/59) was significantly (P < 0.01) lower than from epididymal sperm (50.0%; 22/42). Electroejaculation using a rectal probe had little effect on motility and fertilization capacity of mouse epididymal sperm, whereas the presence of seminal plasma decreased motility and prevented fertilization.