From 1976 to 1979 a prospective study was run at the Women's Hospital of Heidelberg in which every women was registered who attended the hospital before the 20th week of pregnancy. After delivery the infants' development was followed up to four years. During this time 404 women received fenoterol and 74 of them had premature deliveries. While 20% of the women were primarily treated with fenoterol before the 20th week of pregnancy (threatened abortion, cerclage), 80% received the drug in the 2nd and 3rd trimester (premature contractions, abnormal fetal heart rate pattern, premature opening of the external os etc.). Risk factors and early childhood development were compared with 465 women seen in the same time who had never needed fenoterol. The data of the patients' history, the course of pregnancy, and the state of the newborn, revealed that the risk of premature delivery in spite of tocolytic treatment was highest in young women, women with low bodyweight, women with a history of miscarriages, women with threatened abortion and women with anaemia during pregnancy. In correspondence with prematurity, the development of these children was delayed. The same factors of risk were demonstrated in women with successful tocolytic treatment and delivery after the 37th week of pregnancy, although their neonates were in a markedly better state. Early childhood development in this group did not differ from that in the group of women with deliveries after the 37th week and without tocolytic treatment.