The effects of terguride on the uterotonic activity of rat's uterine stria were investigated by means of a standardized isometric method of measuring in vitro the contractility of uterine muscles. The uterotonic activity of the given preparation depends on its concentration and on the phase of uterine cycle. The uterotonic activity makes 71.4 U.mg-1 in the range of terguride concentrations from 10(-7) to 10(-5) mg per ml. Used at higher concentrations, the uterotonic activity of terguride is very low. Spontaneous contractions are moderated and the tone of uterus is decreased by terguride administration.