1. The effect of pH on lactate uptake was studied in perfused liver of rats starved for 48 h.
2. At both low pH (6.8) and normal pH (7.4) lactate uptake was a linear function of lactate concentration in input medium in the range 0.4–1.5 mmol/l.
2. In the lower concentration range (0.4–0.8 mmol/l) the rate of lactate uptake was 30% higher at pH 6.8 than at pH 7.4.
4. At pH 6.8 lactate uptake was independent of whether Pco2 was 2.7 or 5.3 kPa.
5. We suggest the increased rate of lactate uptake at low pH and concentrations lower than 0.8 mmol/l was due to the stimulatory effect of H+ on the lactate carrier.