The effect of HLA on varicella-zoster virus (VZV)-specific lymphocyte transformation (LTF) was studied in 100 normal immune adults and 64 children who were immunized with live attenuated varicella vaccine. In the normal adults, a statistically significant association was observed between low responsiveness and the presence of A2 (p less than 0.025), and also between high responsiveness and the presence of Aw24 (p less than 0.05). A similar but clearer association, i.e. low responsiveness with A2 (p less than 0.005) and high responsiveness with Aw24 (p less than 0.025), was observed in the vaccinated children. In these children, Aw31 was also found to be related to low responsiveness (p less than 0.05). These results suggest that the VZV-specific cellular immune response is in some way influenced by HLA.