Viral infections that occur in patients with primary immunodeficiencies are summarized. These viral infections include: Echovirus, poliovirus, varicella zoster, non-A non-B hepatitis and hepatitis B. Cases of X-linked lymphoproliferative syndrome associated with Epstein-Barr virus infection and congenital rubella syndrome are also reviewed. In the second part of the paper, retrovirus (HIV) isolations from blood mononuclear cells of 3 out of 31 patients with common variable hypogammaglobulinemia are reported. This supports the concept that some of the non-familial "primary" immunodeficiencies may be due to retrovirus infections.