The evaporation rate (ER) from the skin was measured in 40 jaundiced preterm infants born at less than or equal to 34 weeks of gestation. The baseline measurements were executed in both the right and left side in 3 positions: upper arm, back and lower leg. The patients were randomly recruited to a treatment or a control group. The treatment group received 3.0 ml of clear topical ointment just before phototherapy. Conventional phototherapy was placed above the incubators in both groups. ER and ambient skin temperature were measured at the same point at 30 minutes and 5 hours during phototherapy. In the control group, ER was increased by 8.0 per cent (P value = 0.01) and 14.5 per cent (P value < 0.001) at 30 minutes and 5 hours during phototherapy, respectively. In the treatment group, clear topical ointment decreased ER by 19.2 per cent (P value < 0.001) and 13.2 per cent (P value = 0.003) at 30 minutes and 5 hours during phototherapy, respectively. Ambient skin temperature during phototherapy was increased significantly (P < 0.01) in both groups. Serum microbilirubin difference of pre and post phototherapy at 24 hours of phototherapy between the 2 groups was not significantly different (P = 0.38). The authors concluded that conventional phototherapy, in premature infants nursed in an incubator, increased transepidermal water loss (TEWL) significantly and the application of clear topical ointment on the skin of jaundiced preterm infants receiving conventional phototherapy in incubators reduce TEWL significantly, without effect on serum microbilirubin.