Two structurally unusual indolinones containing a spiro-fused cyclopropane and an isonitrile have been isolated from the cells of a cultured cyanobacterium. In a search for inhibitors of arginine vasopressin binding, the unusual indolinones 1A and 1B have been isolated from the cells of a cultured cyanobacterium belonging to the genus Fischerella (ATCC 53558). The structures were elucidated by IR, NMR, and mass spectral analysis and the stereochemistry and absolute configuration of 1A established with single-crystal X-ray diffraction analysis.