Field studies using a chamber technique to measure emissions of nitrous oxide (N2O) showed that the N2O emissions induced by fertilization of soil with anhydrous ammonia (180 kg N ha-1) were markedly reduced by addition of nitrapyrin [2-chloro-6- (trichloromethl)-pyridinel> to this fertilizer. The emission of N2O induced by application of anhydrous ammonia in the fall was reduced 63% by addition of nitrapyrin at the rate of 0.56 kg ha-1. The corresponding reduction when nitrapyrin was added to anhydrous ammonia applied in the spring was 87%. These observations indicate that nitrapyrin has potential value for reduction of the N2O emissions induced by nitrogen fertilization of soils and the possible adverse effects of these emissions on our climate.