A major function of prostatic epithelial cells is production, accumulation and release of citrate which is present in large amounts in the gland and prostatic fluid (Costello and Franklin,1991). The level of citrate is reduced in prostate cancer and almost disappears in metastatic disease (Costello et al. 1999). Using PNT2-C2 cells as a model, we have recently characterised a novel K+-dependent citrate transporter that appeared designed primarily to release citrate (Mycielska & Djamgoz, 2004). In contrast, in PC-3M cells, a Na+-dependent citrate uptake mechanism was also present. Here, we have determined the effects of exogenous citrate on cellular behaviours involved in the metastatic cascade. PNT2-C2 and PC-3M cells were plated on 35 mm Petri dishes (for adhesion and motility) or 24-well plates (for endocytic membrane activity) and preincubated with 0.1 to 10 mM Na+ citrate (in normal growth medium) for 24 and 48 h. Single-cell adhesion was measured using a specifically designed device (‘SCAMA’), endocytic membrane activity was quantified by spectrophotometric measurement of horseradish peroxidase (HRP) uptake, and motility was determined using the ‘wound heal’ method (Fraser et al. 2003). Each experiment was performed at least 3 times. Data were analysed by t-test and are presented as mean percentage changes ± SEM. Preincubation of the normal prostate epithelial PNT2-C2 cells with citrate did not result in any significant change in any of the functional assays performed. On the other hand, PC-3M cells were sensitive to extracellular citrate. After 48 h of preincubation in 10 mM Na+ citrate, their motility was enhanced by 16 ± 5 % (p=0.026, n=5), adhesion was reduced by 50 ± 8 % (p<0.001, n=3) whilst HRP uptake was increased by 45 ± 16 % (p=0.038, n=3). These effects were dose dependent. Short term incubation (35 min) had no effect on HRP uptake by either cell line, which would suggest that the effects were likely to involve cellular metabolism. These results show, for the first time, differential sensitivity of normal and strongly metastatic prostate epithelial cells to extracellular citrate. Whilst normal cells cannot utilise the excess citrate, strongly metastatic cells can take up and use citrate probably as an additional source of energy in enhancing metastatic behaviour.