96 Elevated plasma homocyst(e)ine (tHcy) is an independent risk factor for cardiovascular disease. Cross sectional data have suggested an inverse relationship between plasma homocyst(e)ine and physical activity, but this has not been investigated in intervention studies. This randomised cross-over trial investigated the acute effect of a 30 minute bout of submaximal treadmill running (70/% VO2PEAK) on tHcy in healthy adults (male n=8, female n=3; 22-39yrs) who reported regular (>2 occasions per week) vigorous intensity exercise. Subjects were randomly allocated to perform either exercise or control (30 minutes quiet rest) conditions first. Each condition was separated by a period of at least 48 hours. Subjects consumed no food and drink (excluding water) for 6 hours prior to investigation. Blood was collected from an antecubital vein 15 minutes before (BL) and 2 (T1), 10 (T2) and 30 (T3) minutes post-exercise; control bloods were collected over the same timescale. Blood samples were immediately centrifuged and plasma tHcy analysed by HPLC. Haematocrit was used to estimate changes in plasma volume. The mean (s.d.) tHcy corrected for plasma volume changes pre and post exercise are shown in the table.TableWilcoxon matched pair tests were used to test for differences between tHcy concentrations before and after the exercise bout and for differences between exercise and control days. No significant differences were found between baseline and follow-up tHcy levels for either condition. This study has demonstrated that a single bout of sub-maximal exercise does not alter tHcy levels. Further research is required to determine the nature of the relationship between exercise and tHcy.