the purpose of this study was to examine the relationship between lactate concentrations derived from three sources: whole blood (wbla), plasma (pla) and total blood (tbla) during an incremental bicycle test to exhaustion. regression equations were computed enabling the prediction of one source from another. thirty-two male subjects (16-25 yrs) participated in this study. subjects performed a graded bicycle ergometer exercise test to exhaustion. consecutive blood samples were drawn via an indwelling venous catheter at two minute intervals throughout the test, immediately post, and 5 minutes post exercise. blood was analyzed for: wbla, pla, tbla (ysi lactate analyser model 23l), hemoglobin, hematocrit, bicarbonate and ph. correlations were calculated for all variables. simple and multiple regression equations were computed across exercise intensities. a one-way anova was performed to determine if any significant differences existed between these three indices. this study illustrated that wbla, pla and tbla concentrations, differed significantly and as exercise intensity increased so did the discrepancy. the regression equations were pla=1.568(wbla) + 0.149; wbla=0.887(tbla) + 0.015; pla=1.208(tbla) + 0.093. although highly correlated to lactate values, the predictor variables: hemoglobin, hematocrit, bicarbonate and ph did not enhance the prediction equation.