Incubation of O-alpha-L-dihydrostreptose (1 leads to 4) streptidine 6-phosphate (I) with a protein-free extract from Streptomyces griseus as endogenous donor and a cell-free extract from this organism led to formation of dihydrostreptomycin 6-phosphate (II). The product was identified by paper chromatography and by its degradation to dihydrostreptobiosamine (III). II was not formed when either the donor solution or the dialysed cell-free extract was omitted. The results corroborate the role of I as intermediate in streptomycin biosynthesis. The synthesis of I from dTDP-L-dihydrostreptose, streptidine 6-phosphate and a dihydrostreptosyltransferase from S. griseus has been shown previously.