Ejaculated, density purified, human spermatozoa were exposed to 900 MHz GSM mobile phone radiation at two specific absorption rate levels (SAR 2.0 and 5.7 W/kg) and examined at various time points post exposure. Change in sperm mitochondrial membrane potential was analyzed using flow cytometry. Sperm motility was determined by computer assisted sperm analysis (CASA). There was no effect of 900MHz GSM radiation on mitochondrial membrane potential. This was also the case for all kinematic parameters assessed at SAR of 2.0 W/kg. However, two kinematic parameters (VSL and BCF) were statistically significantly altered after the exposure at SAR 5.7 W/kg. Effects seen cannot be ascribed to heating, as the temperature did not increase by more than 0.3ºC. A thorough investigation at lower SAR levels is required to determine the extent of the influence of RF-EMF on human sperm motility.