A total of 101 preterm infants between 26 and 37 weeks' gestation who received BCG vaccination at birth were evaluated between two and four months after vaccination. Altogether 32% of these infants had no visible BCG scar. All infants were then tested with tuberculin purified protein derivative (PPD) but only 70 returned for the test to be read 48-72 hours later. The test was negative in 22 (31%) and there was an induration of < or = 5 mm in another 26 (37%) of the infants. Of 22 infants with no BCG scar, 19 (86%) had an induration of < or = 5 mm. In infants with a positive BCG scar a significantly higher number had an induration of PPD > 5 mm. There were no significant differences between the rate of scarring and tuberculin conversion in the infants born before or after 32 weeks' gestation. It is considered that routine BCG vaccination at birth on preterm infants is not indicated until a much larger study has been performed.