During hypertonic saline induction, the evolution of intrauterine pressure, the oxytocin response and abortion were delayed in naproxen-treated patients. The PG synthesis inhibitors naproxen, mefenamic acid and ibuprofen decreased the high uterine resting pressure ('tone'), the frequency of contractions but not always the active pressure ('amplitude') in dysmenorrheic patients, with a coincident decrease in pain. The naproxen-sodium treatment decreased prostaglandins F and E in menstrual blood and uterine jet washings by 60--80 per cent.