Morphine can be used to treat pain in preterm neonates with CPAP because of its analgetic potency; however, it is known to induce apnoea. To evaluate this risk of apnoea. We retrospectively analysed 91 preterm neonates with CPAP who received morphine intravenously. The incidence of apnoea 4 h before and after morphine administration was compared. The data were analysed for three dosage groups (<0.01, 0.01-0.03 and 0.03 mg/kg) and according to the incidence of apnoea before morphine application. In the whole group (gestational age 29.1+/-2.9 wk, morphine dosage 0.017+/-0.01 mg/kg) we did not find differences in apnoea before and after morphine (0.9+/-1.8 vs 1.1+/-1.8 apnoea). The only significant increase in apnoea was seen in the subgroup of patients receiving > 0.03 mg/kg (0.3+/-0.67 vs 1.5+/-2.5 apnoea). Interestingly, we found a significantly delayed increase in apnoea in the fourth hour. Morphine in preterm infants with CPAP is not widely accepted practice until further randomized studies evaluate efficacy and safety. Morphine in a low dosage (<or=0.03 mg/kg) did not significantly increase the apnoea rate in CPAP-treated preterm infants. For clinical work, it is very important to note that morphine-related apnoea may appear with a delay of approximately 4 h.