Two one-year-old, mature upflow anaerobic contact filters of the same design and efficiency were acclimatized to tapioca starch waste water. One of the filters was drained off carefully avoiding the entry of air into the filter, and removing suspended biomass. Thus this filter had only attached biomass growth whereas the second one had both attached and suspended biomass. Then both the filters were fed with the waste water starting at a loading rate of 16.0 kg COD m-3d-1 and going down by stages to a loading rate of 1.33 kg COD m-3d-1. Based on the COD reduction data obtained from both the filters, the percent attached biomass activity was found to vary from 72 to 82% out of the total biomass activity. The samples collected from different depths of the filters indicated that in anaerobic filter the attached activity is higher at the bottom and decreased with height of the bed. In this paper the details of the findings are presented.