The dynamics of particle-associated bacteria (PAB) in a tropical estuary, Zuari, in Goa on the west coast of India, was studied for a year from September 1997 to October 1998. Bacterial abundance, productivity and enzymatic activities were measured at fixed station in the estuary. The study period covered pre-monsoon (February to May), southwest monsoon (June to September) and post-monsoon (October to January) seasons. Particulate organic carbon ranged from 0.5 to 17.5 mg C l u-1. Particles of size range is greater than 3 to less than 220 mu m were the most abundant, were rich in organic carbon (approx. 60%), and formed 55% of the suspended load (ave. approx. 0.1 g l u-1) in the estuary. PAB ranged from 8.8 x 10 u7 to 3.9 x 10 u10 l u-1 and the waters close to the sediment had a higher abundance than the surface waters. PAB varied seasonally and accounted for 20 to 80% of the total bacterial population. The mean rate of production as measured by u3H-Thymidine incorporation was 70 mu g C l u-1 d u-1 in the surface and 35 mu g C l u-1 d u-1 in the bottom waters. Monthly production varied by 2 orders and was not coupled to abundance. However, high production during the monsoon was fuelled by allochthonous input of organic matter. No linear relationship was observed between biological parameters and other measured environmental parameters except for temperature, which showed a linear relationship with PAB and particle numbers. The bacterial carbon demand (BCD) at the station was higher than the primary production (PP) and was met by allochthonous input. The study demonstrates that the PAB dynamics were determined by the availability of substrates and resuspension of sedimented materials