The results of a study concerning the treatment of acute menace of preterm labor are given: beta-mimetics were administered intravenously in all cases (44) and micronized progesterone or placebo was administered orally after classical double-blind randomization (22 cases in each group). The mean index of pregnancy prolongation was the same in both groups. However the mean duration of the intravenous perfusion and the mean quantity of beta-mimetics administered intravenously were significantly reduced in the progesterone group (P less than 0.01). The mean duration of hospital stay was also significantly reduced (P less than 0.05). Cost and risks are finally significantly lessened.