AbstractIn experiments on bovine mesenteric arteries under anaerobic conditions tone‐promoting drugs gave rise to contraction and to augmentation of the lactic acid production. Under certain experimental conditions it was possible to dissociate these effects. In the presence of glucose, dihydroergotamine selectively inhibited the contractile effect of adrenaline without influencing its stimulatory effect on lactic acid production. Replacement of the Tyrode solution with 6 per cent dextran solution resulted in selective inhibition of the contractile effects of adrenaline and histamine but did not interfere with the stimulation of the lactic acid production. Potassium ions selectively stimulated the contractile process, while the lactic acid production diminished during the contraction phaseper se. On substrate‐depleted arterial muscle, potassium ions had a more pronounced stimulatory effect than did adrenaline, histamine or barium ions. It is assumed that, despite the correlation of the contractile effects of tone‐promoting drugs to the stimulation of lactic acid production, these two factors are activated by separate mecha