The action of some antispasmodics (hyoscine, N-butyl-hyoscine, octammonium and diprosine) was studied in vitro and in vivo in the guinea pig and in the dog. The organs tested were: stomach, ileum and terminal colon, activated by electrical (parasympathetic, sympathetic, transmural) and chemical (acetylcholine, histamine, 5-hydroxytryptamine, nicotine) stimulation. The displacement of dose/response lines to agonist, the effective doses 50%, the pA2 and the relative estimated potencies were calculated. On the whole, the antispasmodic power of the drugs tested should be evaluated as a function of: (1) use of in vitro and in vivo techniques; (2) type of stimulation applied; (3) time of action; (4) general toxicity of the substance. The results were discussed in connection with employment in clinical pharmacology and therapeutics.