Thiarubrines are dithiacyclohexadiene polyacetylenes displaying considerable antimicrobial activity. A culture that accumulates these compounds was obtained by selection of red-colored areas from crown gall tumor cultures of Chaenactis douglasii. The tumors were induced by A. tumefaciens strain A277. The main acetylenic products found were two thiarubrines, A and B, and their corresponding thiophenes. Average yields of thiarubrines and thiophenes were 2.5 and 0.24 mg/g dry weight respectively, which are similar to the values seen in intact plants. The products accumulate in intercellular spaces arranged around a core of vascular tissue, forming red nodules of varying size. The structures crudely resemble the tissue organization of the roots of this plant, the only organ where these compounds accumulate. Formation of rootlets, however, does not take place at any stage during the growth of the tumors. Evidence is presented suggesting that the accumulation of these polyacetylenes by the tumor line is not a direct result of cellular transformation but a secondary effect of the existing degree of tissue differentiation. © 1986, Gustav Fischer Verlag, Stuttgart. All rights reserved.