 Without the use of preventative measures, the risk of mother-to-child transmission MTCT of HIV-1 is estimated to vary between 25 and 48. The regimen of single dose of nevirapine to the mother just before delivery and a single dose of nevirapine to the newborn within 24 - 72 hours after birth reduces the risk of MTCT by 50, is affordable in many situations and is therefore standard of care in many African countries, like Tanzania. Recent studies, however, have shown that this single dose to the mother can induce the occurrence of nevirapine resistance in a large number of mothers. The mechanism of occurrence of nevirapine resistance already after a single dose is most likely related to the long elimination half-life of the drug. The subtherapeutic plasma levels present the perfect environment for the occurrence of resistance as the concentrations are subinhibitory for several days. 