Objective: To determine in preterm infants with a patent ductus arteriosus (PDA) the effect of indomethacin treatment on spontaneous motor activity. Study Design: Motor activity was assessed from repeated videotape recordings in 32 preterm infants (less than or equal to 33 weeks gestation). Sixteen infants required indomethacin therapy for treatment of PDA, 16 were control infants, matched for gestational age. Indomethacin (0.2 mg/kg i.v. in 5 min) was given thrice, with an interval of 12 h. One-hour record ings were made immediately before and immediately after the first dose of indomethacin and 24 h later before and after the third dose. The same recording schedule was used for the control infants. Th effects of indomethacin on quantity and quality of spontaneous motor activity were examined. Results: A significant reduction in the quantity of several spontaneous movement patterns and an increase in the occurrence of rest periods were found following the first indomethacin administration (p <0.01). Concerning the quality of general movements, a reduction in the speed was found (p <0.05). Both effects were not found after the third indomethacin administration. Conclusion: In preterm infants with a PDA, treatment with indomethacin leads to a transient reduction in the quantity of spontaneous movement patterns and to a decrease in the speed of general movements. We recommend a cautious use of bolus indomethacin for the treatment of PDA. Copyright (C) 2000 S. Karger AG, Basel.