Abstract The antibiotic complex of a new heptaene polyene produced in Streptomyces griseoviridis, which is antagonistic to phytopathogenic fungi, was analysed by high-performance liquid chromatography (HPLC) and monitored with a diode-array detector. For reference six known heptaenes were also assayed. The individual components were separated on ODS Hypersil C 18 using gradient or isocratic elution. Gradient elution was performed using 0.005 M EDTA buffer modified with methanol and acetonitrile. Isocratic separations were made with 0.05 M ammonium acetate modified with acetonitrile. Both elution systems separated the main components, but the gradient system eluted the long-retained components faster. The chromatogram of the heptaene isolated from S. griseoviridis was compared with those of aureofungin, candicidin, candimycin, hamycin and trichomycin. The heptaene synthesized by S. griseoviridis is a candicidin type, as indicated by HPLC.