HASKELL et al isolated amicetin (I), bamicetin (II) and plicacetin (III) from Streptomyces plicatus. We isolated a fourth antibiotic, norplicacetin (IV), from a streptomycete isolated from a soil sample from Ghana. The organism, closely related to or identical with Streptomyces plicatus (deposited as NCIB 11305), produced fine aerial hyphae carrying more than 10 grey, smooth-walled spores in unbranched chains ending in a loop or open spiral, had yellow vegetative growth, grew on L-arabinose, D-fructose, D-galactose, D-glucose, L-rhamnose, D-mannitol, D-xylose and i-inositol but not on raffinose and sucrose, and was inhibited by streptomycin sulphate. Antibiotic production was assayed by agar diffusion (cup-plate) with Staphylococcus aureus Oxford H strain VI; thin-layer silica gel chromatography and bioautography were used to detect and quantify the antibiotics. The organism was cultured in shake flasks (medium containing sucrose, milled soya bean, beet molasses, etc.) and a 5-litre fermenter. Fermented broth was centrifuged, the supernatant extracted with n-butanol, and the extract purified via silica column chromatography and Sephadex LH2O chromatography. Compound C was isolated as white needles (m.p. 168-171°C, [α]28D +125° (c 1, methanol)); its UV spectrum was identical to plicacetin, mass spectrum (field desorption) showed M+ m/e 503 (suggesting molecular formula C24H33N5O7), and NMR spectrum revealed a singlet for 3 N-CH3 protons (vs. 6 in plicacetin), identifying it as norplicacetin (IV), an undescribed member of the amicetin group. Antimicrobial spectrum showed norplicacetin had moderate activity against Gram-positive bacteria and mycobacteria, resembling plicacetin.