The invention provides an agent against HIV and/or related viruses, comprising CD4 or a CD4-like substance and an H2 histone or an H2 histone-like protein. The content of the CD4 or CD4-like substance is preferably less than the antivirally effective dose of that substance alone. The invention also provides an H2 histone or an H2-like protein, for use in a method of medical treatment, in particular against HIV and/or related viruses, and also for use in the manufacture of a pharmaceutical compos...