In a randomized trial intramuscular ritodrine followed by oral ritodrine treatment and bed rest was compared with placebo and bed rest in the treatment of 99 cases of preterm labor. The ritodrine treatment did not have a statistically significant effect on birth weight, gestational age, or the incidence of low birth weight. However, it did inhibit preterm labor in the initial stage, resulting in a gain of a few days to a few weeks in length of gestation. This gain may be valuable. Where necessary, advantage can be taken of it to transfer the mother before delivery to a more specialized hospital with a neonatal intensive care unit or to administer steroid treatment to promote fetal lung maturation. No serious side effects were recorded. The intramuscular route is recommended because large fluid infusions are avoided and treatment can easily be started before the patient is transported from home to hospital.