The steroid hormone progesterone is released from cumulus cells surrounding the oocyte and is known to influence the physiology of sperm as it moves towards the uterine tubules. Progesterone induces hyperactivation, the acrosome reaction and chemotaxis in capacitated human sperm. Micromolar, but not nanomolar, concentrations of progesterone induce the acrosome reaction in capacitated boar sperm but non capacitated cells are unresponsive (Barboni et al., 1995; Jang & Yi, 2002). However we are unaware of any reports of the effects of progesterone on the mobility of non capacitated and capacitated boar sperm. In this study we sought to address this by using a mobility assay that monitors sperm penetration through an inert cell-separation solution (Vizcarra & Ford, 2006). Semen samples, diluted in Trixcell extender solution, were obtained commercially. Samples are from PIC 337 champion species of boar. The mobility assay involved using spectrophotometry (550nm) to measure the rate at which sperm penetrated through an inert cell-separation solution alone or containing increasing concentrations of progesterone (0.1 – 100nM). The cell-separation solution was placed in the cuvette and 1×10 8 non capacitated sperm cells were carefully loaded onto the surface of the solution and then incubated at 37°C. Absorbance readings were taken over time to monitor the progression of sperm through the solution. Heat inactivated sperm were used in the negative control and did not penetrate the solution. The positive control involved mixing 1×10 8 sperm cells with the cell separation solution before loading into the cuvette. Statistical significance was determined using general linear mixed effect test (IBM SPSS statistics) and data are presented mean ± SEM. Curves are fitted using non-linear regression model and Km values (minutes) represent the time at which absorbance was half maximal (Graphpad Prism). Cells maximally penetrate the solution over 50 minutes. 100nM progesterone significantly (P<0.001) increased the mobility of sperm cells causing a doubling in the rate at which the cells penetrated through the cell-separation solution (control Km = 19±3; +100nM progesterone Km = 9±1, N = 30 assays in each case using cells from at least 3 different boars). Parallel experiments were conducted to assess the acrosome status before and after progesterone treatment. Non capacitated cells exposed to progesterone for 50 minutes showed a decrease in acrosomal integrity (77.23.6 at t=0; 64.08.2% at t=50, n=3). The non-capacitated status of the cells was confirmed by western blotting for total protein tyrosine phosphorylation. These data demonstrate for the first time that progesterone can enhance mobility of non capacitated boar sperm. Our immediate aim is to examine if capacitation increases the sensitivity of boar sperm cells to progesterone.