We previously 2* reported the isolation, structural elucidation and biological properties of new phosphodiesterase inhibitors, the obscurolides A₁ to A4 (1 to 4) from the cultures of Streptomyces viridochromogenes (strain Tü 2580). A careful search for minor components by chemical screening methods 3)4) revealed eight further members of the obscurolide-complex 2) (Scheme 1). They were assigned to the B, C and D series signifying their differences in the polyketide moiety (C-1 to C-8), whereas the subscripts indicated the oxidation level of the functional group at C-4'. In this paper the isolation, physico-chemical and biological characterization of these new compounds are described. All obscurolides were isolated as diastereomeric mixtures at C-7 (A and C series) and C-5 (B series), respectively. Only in the cases of 5/6 and 9/10 could the isomers be separated.