The purpose of this study was to determine the effect of blood flow on net lactate uptake (L) at constant elevated blood lactate concentration and metabolic rate in the in situ dog gastrocnemius-plantaris (GP) muscle. In all experiments, an infusion of lactate/lactic acid at a pH of 3.8 established a blood lactate concentration of 10-13 mM while maintaining normal blood gas/pH status as the GP was stimulated to contract with twitches at 1 Hz. In series 1 (n = 14), blood flow (ml.kg-1.min-1) was controlled by a pump at either 1) the spontaneous level for 1-Hz contractions (control flow = 332 +/- 23) or 2) a level estimated to be approximately 65% greater (high flow = 543 +/- 42). In series 2 (n = 7), perfusion pressure was varied during 1-Hz contractions. Four different perfusion pressures (80, 120, 155, and 180 Torr) were presented to each GP preparation, resulting in mean flow rates of 308 +/- 34, 419 +/- 30, 492 +/- 37, and 646 +/- 30 ml.kg-1.min-1. Increasing blood flow had no significant effect on net L in series 1. Similarly, there was no significant change in net L across the first three perfusion pressures/flow rates in series 2. However, net L (mmol.kg-1.min-1) was significantly increased in the highest perfusion pressure/flow rate period (from 0.335 +/- 0.029 at 80 Torr to 0.431 +/- 0.034 at 180 Torr). This study suggests that blood flow may have an independent effect on net L at the upper extreme of the normal blood flow range during contractions but very little effect over a fairly wide low-to-middle range of flow rates.