Three tantazole-related compounds, viz. didehydromirabazole A (1 ) and mirabazoles B (2) and C (3), have been isolated as minor components from Scyfonema mirabile (Dillwyn) Bornet (strain BY-a-l) and their structures elucidated.Four classes of cytotoxins are associated with terrestrial Scytonema mirabile (Dillwyn) Bornet (BY-8-i), viz. scytophycins,z tantazoles,3 mirabimides,' and mirabilene isonitriles.5 The most potent cytotoxin is tolytoxin (6-hydroxy-7-0-methylscytophycin B),*,e which interestingly shows murine and human solid tumor selective cytotoxicity in the Corbett assay. 7 Tantazole B, one of two major tantazoles in the alga, also shows solid tumor selective cytotoxicity, albeit murine only, in the Corbett assay.JJ We report here the isolation and structure determination of three tantazole-related compounds, didehydromirabazole A (1 ), another murine solid tumor selective cytotoxin,7 and mirabazoles B (2) and C (3) from S. mirabile BY-a-l. The mirabazoles consist of four successive 2,4-connected thiazoline/thiazole rings terminated at one end of the molecule by an isopropyl group on C-2 of ring A. Methyl groups are present on C-4 of rings A and C, but may or may not be substituted on C-4 of rings B and D. The mirabazoles, however, lack the oxazole ring E typically found in the tantazoles and attached via C-2 of ring E to C-4 of ring D.