With improved survival of very low birth weight infants (VLBW, <1500 grams) fungal sepsis has become an important contributor to morbidity and mortality. Disseminated fungal infections now occur in 3-4% of VLBW infants. We hypothesize that Candida albicans colonization and subsequent invasive disease in VLBW infants is due to vertical transmission. We collected vaginal, rectal, hand and oral specimens for fungal cultures within 24 hours of, or at delivery from mothers who gave birth to VLBW infants. Oral, inguinal, and rectal specimens for fungal cultures were obtained from infants at birth and then weekly for 12 weeks or until discharge. C. albicans isolates were identified by standard methods and then typed into strains by DNA fingerprinting using the CARE-2 probe. We have enrolled 47 mother/infant (M/I) pairs including three sets of twins. Thirty-two (68%) mothers were colonized with C. albicans. Of the 33 infants born to these colonized mothers, 15(45%) became colonized with C. albicans and 5 (15%) became colonized with a non-C. albicans species. Thirteen of the 18 infants colonized by C. albicans were so by 1wk of age. All 5 infants colonized with non-C. albicans became so at≥ 2 wks of age. Additional 3 infants colonized with C. albicans were born to non-colonized mothers. DNA fingerprinting using the CARE-2 probe revealed a wide variety of banding patterns denoting different maternal strains. Of 11 colonized M/I pairs tested there was virtual identity in the banding pattern for 8 (73%) pairs, documenting colonization with the same strain. Approximately 70% of mothers were colonized with C. albicans. Most C. albicans colonized infants were born to colonized mothers and these became colonized by 1 wk of age, suggesting a vertical mode of transmission. Vertical transmission was confirmed in 8 M/I pairs studied using DNA finger printing for strain identification.