Production of neomycin by a mutant strain of Streptomyces marinensis, under solid state fermentation was optimised. Various substrates were used to study their effect on neomycin production. Wheat rawa was found to be better for optimum production of neomycin. The maximum neomycin yield (10 755 mug/g substrate) was achieved with optimised process parameters such as coarse size of wheat rawa with raspberry seed powder (10% w/w) as additional nutrient, initial moisture content of solid substrate 80%, initial pH of the medium 7.5, incubation temperature 30degreesC, inoculum size 0.5% w/w dry cell mass equivalent and 10 days of fermentation time. One hundred and forty percent of higher production was achieved after optimising the process parameters. (C) 2002 Published by Elsevier Ltd.