Over a 13-month period 52 neonates (10% of those admitted to the Mersey Regional Neonatal Intensive Care Unit) were found to be colonised with the ascosporagenous yeast Hansenula anomala. 8 babies became infected, all but 1 of whom were heavily colonised before infection. 7 of the 8 infected babies were of very low birth-weight (less than 1500 g). All 8 had multiple problems associated with low birth-weight and prematurity and were kept in the intensive care unit. 5 babies had fungaemia, 2 had fungaemia and ventriculitis, and 1 had ventriculitis only. In each case H anomala was the sole pathogen isolated. Anti-Hansenula antibodies developed in 5 babies within 3 months of infection. Infected babies were successfully treated with a combination of 5-flucytosine and amphotericin B. Despite extensive searches the babies appeared to be the only reservoir of the yeast.