The effect of lactate infusion on pCO2 and respiration rate was studied in two differently instructed groups of healthy volunteers in a double-blind, placebo-controlled, cross-over study. Both groups showed a significant decrease in alveolar pCO2 after lactate but not after placebo. This was accompanied by an increase in respiration rate in those subjects who had expected to become anxious and by a decrease in respiration rate in those who had expected to experience pleasant excitement.