Here we describe the features of a peptide that was selected from the human immunodeficiency virus Type 1 (HIV-1) Integrase (IN) peptide library which interacts with both, the viral Rev and IN proteins. Because of its ability to stimulate the IN enzymatic activity this peptide was designated INS (IN stimulatory). Modification of its amino acid sequence revealed that replacement of its C-terminal lysine by glutamic acid (INS K188E) converts it from a stimulatory peptide to an inhibitory one. Both peptides promoted the dissociation of a previously described complex formed between Rev and IN whose formation results in IN inactivation. INS and INS K188E penetrated HIV-1-infected cells and caused stimulation and inhibition of viral genome integration, respectively. Using cultured cells infected with a DeltaRev HIV revealed that INS can directly activate the viral IN. These results suggest that the stimulatory effect of INS in wild-type virus-infected cells is due to a dual effect: it dissociates the inactive Rev-IN complex and directly activates the free IN.