Sulfachloropyridazine (SCP), an antibiotic used in aquaculture and in animal husbandry, is a common contaminant in surface and groundwaters. Two types of microbial reactors were evaluated as methods for removing SCP from flowing water. One type of reactor evaluated was a nitrogen-limiting biobarrier; the other a slow-sand-filter. Results showed that the soybean oil-fed, nitrogen-limiting biobarrier was not very effective at removing SCP from flowing water. When supplied with flowing water containing 2.4 mg l(-1) SCP the nitrogen-limiting biobarrier removed similar to 0.6 mg l(-1) SCP or about 28% of that present. SCP removal by the nitrogen-limiting biobarrier may not have been biological as abiotic removal was not ruled out. More efficient biological removal was obtained with the slow-sand-filter which reduced the SCP levels from 2.35 to 0.048 mg l(-1), a removal efficiency of similar to 98%. High levels of nitrate nitrogen, 50 mg l(-1) N, did not interfere with the removal processes of either reactor suggesting that SCP was not being degraded as a microbial nitrogen source.