As the chemical environment of semen diluents can have a profound effect on sperm quality, we examined the effect of temperature and pH on the motility and viability of sperm in the ostrich. Semen was collected from four males, each male being replicated three times. Ejaculates were diluted and incubated for 10 min at 20 degrees C and 40 degrees C in four different buffers, temperature adjusted at pH 6, 7, 8 and 9 respectively. Average path velocity (VAP), curvilinear velocity (VCL), straight-line velocity (VSL), linearity (LIN), beat cross frequency (BCF) and amplitude of lateral displacement (ALH) were then recorded for each sample using CASA. The viability of sperm was assessed using nigrosin-eosin staining. Sperm incubated at 40 degrees C had higher motility parameters, except for ALH. At 40 degrees C, VAP, VSL and LIN increased with pH while VCL, BCF and ALH were higher for lower pHs. The viability of sperm was not affected by temperature but decreased at pH values > 7. A pH in the neutral range appeared to yield higher quality sperm after in vitro storage at 20 degrees C. However, the effect of different pH levels and temperatures on sperm longevity needs to be investigated further to develop viable ostrich specific diluents. (C) 2012 Elsevier B.V. All rights reserved.