Haemophilus spp. were isolated from the amniotic fluid of eight of 110 consecutive women with preterm premature rupture of membranes (PROM) between 1992 and 1998. Isolates were nontypeable and classified according to biochemical test results as Haemophilus influenzae biotype I (n = 1), biotype II (n = 4), biotype III (n = 1) or biotype IV (n = 2). Primers recognizing specific sequences in the 16S rRNA of the cryptic genospecies of Haemophilus were employed to amplify the DNA of the eight isolates. One isolate classified as Haemophilus influenzae biotype II was confirmed as belonging to the genital cryptic species. Infectious morbidity occurred in five women and two newborns and was associated in most cases with biotype II.