Neomycin production by free and alginate immobilized Streptomyces marinensis cells was investigated in an airlift reactor. Neomycin production was increased two and a half times with immobilized cells. A marginal decrease in neomycin production was noticed with reduced supplementation of carbon source (up to one-fourth concentration). Immobilized S. marinensis particles showed a half-life of 20 days during continuous fermentation in an airlift reactor. (C) 2002 Elsevier Science Ltd. All rights reserved.