Water and nutrient delivery during exercise is determined by the combined rates of gastric emptying and intestinal absorption. Exercise at an intensity that exceeds 70% VO2max results in a reduction in gastric emptying rate, particularly when exercise is of an intermittent nature[1]. It has been suggested that this observation is likely to be due to the reduction in splanchnic blood flow that has been observed during exercise[2]. It has also been suggested that this reduction in splanchnic blood flow is the main mechanism for a number of gastrointestinal complaints observed during exercise[2]. Citrulline, a precursor to L-arginine, increases nitric oxide production and pre-exercise ingestion has been shown to increase blood flow in gut microcirculation and reduce levels of enterocyte damage[3]. The aim of this study was to determine whether pre-exercise citrulline ingesion influenced gastric emptying rate during moderate intensity exercise. Ten healthy male participants aged 21 ± 1 y undertook two experimental trials in a randomised, crossover, double blind, placebo controlled study. Following an overnight fast, participants ingested 100 mL of water with either 6 g of citrulline malate or alanine before a 30 minute rest period. Participants then ingested 600 mL of a commercially available sports drink containing 100 mg 13C sodium acetate, for measurement of gastric emptying rate. They then undertook a 60 minute period of cycle ergometry exercise at an initial intensity sufficient to illicit 65% of age predicted maximal heart rate. Breath samples were collected pre-exercise and at 10 minute intervals throughout exercise to assess gastric emptying rate using the [13C] acetate breath method. Data was analysed using t-tests and two factor ANOVAs where appropriate. Half emptying time (T1/2) of the solution amounted to 45 ± 7 and 47 ± 12 minutes (P = 0.559) during the alanine and citrulline malate trials respectively. Time of maximal emptying rate (Tlag) amounted to 35 ± 5 and 35 ± 6 minutes (P = 0.822) during the alanine and citrulline malate trials respectively. Two factor repeated measures ANOVA on breath delta over baseline data showed no main effect of supplement (P = 0.888), a main effect of time (P < 0.001) and no interaction effect (P = 0.915). Citrulline supplementation has been demonstrated to improve blood flow of the gut microcirculation[3] however the results of this study suggest that 6 g citrulline malate 30 minutes prior to moderate intensity exercise has little effect on gastric emptying rate during exercise. Future studies should focus on the intensity of exercise and/or the dosage of citrulline malate provided.