Purpose: To investigate possible association between the transmission of mutans streptococci and sharing the immune system component Human Leucocyte Antigen (HLA) class II in mother-child pairs. Material and Methods: Plaque samples from 43 mother-child pairs were cultivated and screened for mutans streptococci. In 14 pairs where both mother and child harboured the bacteria, the strains were genotyped by Random Amplified Polymorphic DNA and samples were run on PAGE gels. Analysis of genetic identity between mother and child strains was performed with help of software and Dice similarity index. The distribution of HLA of serogroup DR4 (HLA DR4) was studied in relation to maternal transmission and mutans streptococci colonisation in children. The study hypothesis was that in pairs where both mother and child were HLA DR4 positive, transmission of mutans streptococci was more likely. Results: No correlation between the presence of HLA DR4 in mother and child and maternal transmission of mutans streptococci was established. However, the results showed no linkage between mutans streptococci colonisation and HLA DR 4. Of 15 children with mutans streptococci, 12 were HLA DR4 positive. Conclusion: The result suggests that presence of HLA DR4 could be a predisposing factor for colonisation with mutans streptococci in children. Schlagwörter: colonisation, HLA, mother-child pair, mutans streptococci, transmission