The biological activities of the streptovaricins, members of the ansamycin class of antibiotics, are of continuing interest and we are now investigating the minor components of the streptovaricin complex. In the course of these studies, a new metabolite, tryptophan-dehydrobutyrine diketopiperazine (TDD), was isolated from Streptomyces spectabilis, the organism producing the streptovaricin antibiotics. The structure of TDD was assigned from spectral properties and degradation products. TDD shows weak activity against RNA directed DNA polymerase (reverse transcriptase)-30% inhibition of RLV reverse transcriptase at 200 ug/ml-but it does not have significant in vitro antibacterial activity or inhibitory activity toward Escherichia coli DNA-dependent RNA polymerase.