The occurence of tenuazonic acid (T. A.), which had been isolated from the culture broth of blast fungus, in blast-diseased rice plants was surveyed to ascertain whether or not this substance is one of the vivotoxins. T. A. was detected in four of six samples of blast-diseased rice plants, two of which had relatively high T. A. contents; 379 and 91mg per kg of the samples (dry weight). Besides T. A., coumarin, o-coumaric acid and piricularin were also isolated from blast-diseased rice plants. The molecular formula of the last substance, which was tentatively presented in a previous paper, was corrected to C18H30N2O5 from the results of high resolution mass spectrometry.