Streptomyces sp. WK-2955, a soil isolate, was found to produce a series of new anticoccidial compounds. Four active compounds, designated diolmycins A1, A2, B1 and B2, were isolated from the fermentation broth of the producing strain by solvent extraction, silica gel column chromatography, gel filtration on Sephadex LH-20, and preparative HPLC. Diolmycins inhibited the growth of Eimeria tenella in an in vitro assay system using BHK-21 cells as a host. No schizont in the cells was observed at concentrations of 0.02-2.0 micrograms/ml for diolmycin A1, at 0.2-2.0 micrograms/ml for diolmycin A2, and at 20 micrograms/ml for diolmycins B1 and B2.