The study examines the effects of Roundup (N-(phosphonomethyl) glycine) and N-Serve (2-chloro-6-(trichloromethyl) pyridine) on the culture of soil organisms in a continuous-flow column system. In the study, nitrifying and various heterotrophic bacterial populations were enumerated over a 16-day period. The chemicals Roundup and N-Serve were added at day 8. Heterotrophic bacterial populations increased significantly in columns with 4.2 mg nitrapyrin and 68 mg glyphosate per g dry soil. Numbers of heterotrophs were not significantly different from controls in columns at lower chemical concentrations. Numbers of nitrifying bacteria did not appear to change following treatment, although nitrification was inhibited. Fluorescent antibody analysis of the nitrifying bacteria revealed that Nitrosolobus was more numerous than Nitrosospira and Nitrosomonas. Nitrosolobus increased in number, whereas the other two genera remained unchanged. In the study, the continuous-flow system proved to be both reliable and useful in the culture of nitrifying bacteria. The method is an alternative to traditional techniques for evaluation of the effects of chemicals on microbial biogeochemical cycles.