Investigation on the influence of seasonal changes in physico-chemical factors on particulate matter in the "Bombay High" region from February'85 to January'86 suggests that dominance of physical factors in monsoon largely influence the production of phytoplankton biomass. Ratio of silicate and nitrate to phosphate was 16:16:1 for monsoon and postmonsoon periods. Annual values of particulate carbohydrates, particulate proteins and particulate lipids in surface waters ranged from 40 to 265 mu g l sup(-1), 21 to 56 mu g l sup(-1) and 14 to 51 mu g l sup(-1) respectively. Significant correlation of particulate carbohydrate, particulate proteins and particulate lipids with chlorophyll a suggested that plankton biomass comprised a substantial percentage of these constituent fractions. Almost uniform ratios of particulate lipid to particulate organic carbon (PL/POC) during all the three seasons indicated incorporation of petroleum hydrocarbons in the suspended particles.