Inhibitory effects of Partusisten, Dilatol, Papaverin and Magnesium-sulfat on the activity of smooth muscle were tested in vitro on 18 isolated stripes of rats uteri, exhibiting both a high sensitivity against oxytocin and a distinct spontaneous activity. Minimal inhibitory concentrations of all drugs tested were determined, and their influence on the frequency and amplitude of contraction as well as on lag phase between inhibition and onset of spontaneous activity were registered. Basing on these experimental data conclusions were drawn concerning their clinical relevance.