The prevalence rates of the platelet glycoprotein IIb/IIIa Leu33Pro allele (PLA2), and factor V G1691A Leiden mutation were determined in 109 appropriate for gestational age neonates with grade I intraventricular haemorrhage (IVH) and in 118 IVH-free control infants. The PLA2 allele frequency was 16.4 % in the group of full-term infants with grade I IVH, while it was 9.5 % in the relevant controls (p < 0.005); there was no difference in the PLA allele frequencies on comparing the IVH affected (8.34 %) and unaffected (9.2 %) premature infants. By contrast, the factor V Leiden allele frequency was increased only in the subgroup of premature infants with grade I IVH as compared with the appropriate premature controls (9.25 % vs. 3.34 %, respectively, p < 0.005). These data suggest that besides the factor V Leiden mutation, the PLA2 allele, which has already been suggested to have a role in neonatal alloimmune thrombocytopenia and certain subtypes of adult stroke, can have significance in the development of the events of IVH.