AZT has been shown to be effective in the treatment of AIDS and advanced ARC but not without toxicity. The most clinically significant toxicity is dose related inhibition of bone marrow function. Furthermore, HIV-1 isolates from patients treated for more than 6 months with AZT have now been found which appear to have reduced sensitivity to AZT. The incidence of toxicity and occurrence of virus with reduced sensitivity to AZT may result in the inability to administer AZT long-term to patients with AIDS and advanced ARC. Recombinant soluble CD4 (rCD4) has shown antiretroviral effects and has been shown to be safe when given to AIDS and ARC patients either as a single agent or in combination with AZT.