Part 1A: To find the dose of zidovudine (AZT) that causes less than a 50 percent drop in HIV-1 p24 antigen levels in patients with AIDS and advanced AIDS related complex (ARC); to determine the pharmacokinetics (blood levels) of rsCD4 administered in combination with AZT. Parts 1B and 2: To test for additive or synergistic activity between rsCD4 and AZT as judged by falls in HIV-1 p24 antigen levels; and to evaluate the safety of rsCD4 and AZT in patients with AIDS and advanced ARC.