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.

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