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. Dose response curves for noradrenaline were determined before, during and after pretreatment with a variety of agents. The inhibitory response to noradrenaline on the isolated rat uterus was measured according to its ability to inhibit an acetylcholine induced contraction. . Theophylline, an agent that inhibits phosphodiesterase and increases cyclic AMP levels in the rat, potentiated the response to noradrenaline. . Pretreatment with cocaine had no significant effect on the potentiation of the noradrenaline response by theophylline. . Theophylline potentiated the inhibitory response to nitroglycerine. . Pretreatment with nitroglycerine also potentiated the inhibitory response to noradrenaline. . Theophylline appears to produce a potentiation of the inhibitory effect of noradrenaline on the rat uterus by means of a non‐specific mechanism.