Two pot experiments were performed to study the effects of three pre-emergence herbicides (terbutryn/terbuthylazine, trietazine/simazine and prometryn) and a post-emergence herbicide (bentazone) on nodulation, symbiotic nitrogen fixation, growth and yield of pea (Pisum sativum L.) grown in perlite under nitrogen-free conditions. All pre-emergence herbicides decreased nodulation, total nitrogenase activity, net photosynthesis, leaf area, root and shoot dry weight, nitrogen content and seed yield of peas. The effects of herbicides increased with increase in rate of application. Of the herbicides tested, terbutryn/terbuthylazine and trietazine/simazine had the greatest adverse effects. Pea plant biomass (root plus shoot) was correlated with plant nitrogen content but not total nitrogenase activity. The results of the experiments suggested that the decreased growth of herbicide-treated plants was due to direct effects of the herbicides on peas and not due to indirect effects of the herbicides on rhizobia.