To clarify the relationship between the amount of anti blast substances, momilactones, in rice leaves and the degree of horizontal resistance to rice blast disease, the quantitative estimation of these substances in leaves of several cultivars which are different in their resistance was conducted by GLC. The authentic momilactone A showed Rt 26.8min and momilactone B-TMS showed Rt 21.1min on OV-17 at 213C and N₂ flow rate 45ml/min. While, momilactone A showed Rt 16.4min and momilactone B-TMS showed Rt 22.1min on OV-101 at 188C and N₂ 45ml/min. These results were quite different from the data of the original report of Cartwright et al. The peaks of momilactones A and B-TMS were analyzed by GC-MS and identified. No momilactones were detected in the extracts from the healthy and blast-infected rice leaves of several cultivars. Although eight-times higher concentration compared with that of the original report was subjected to GLC, momilactones could not detect. These results indicate that the amount of momilactones in infected leaves may be quite lower than the amount reported originally.