A modified spectrophotometric method was developed to estimate ioxynil and bromoxynil residues. The method when compared with a14C-tracer method was less sensitive but allowed rapid and accurate estimation of the herbicides.A clay loam soil with high organic matter content, which degraded ioxynil completely to CO2, also degraded bromoxynil completely. Bromoxynil degradation proceeded at a faster rate than that of ioxynil. The half-life of degradation was estimated to be 7 days for bromoxynil and 9–10 days for ioxynil. However, soil microorganisms which degraded ioxynil either completely to CO2or partially did not seem to completely degrade bromoxynil. Degradation products from bromoxynil were detected on thin-layer chromatograms of extracts from pure cultures containing an exogenous carbon source. Complete degradation of bromoxynil and ioxynil in soil could be due to the action of different microorganisms.