Abstract G. Flores-Otero, J. Cueva, E. J. Muñoz-Martínez and C. Rubio-Franchini. Spectrophotometric and chromatographic detection of Karwinskia humboldtiana (tullidora) toxin in rat serum after tullidora ingestion. Toxicon 25, 419 – 426, 1987.—The absorbance spectrum of tullidinol, a tullidora ( Karwinskia humboldtiana) toxin, showed peaks at 260 and 410 nm when dissolved in ethanol; the second peak was linearly related to toxin concentration. Silica gel thin layer chromatograms of tullidinol solutions showed a single, yellow spot with an R f of 0.76. A single dose of tullidora fruit homogenate was orally given to male Wistar rats; the absorbance spectrum of serum from tullidora-treated rats showed peaks at 300 nm and at 410 nm; the second peak was absent in serum from control rats. No spots were detected in chromatograms of normal serum, but a yellow spot with the same R f as that of tullidinol was found in the serum of tullidoratreated rats. We conclude that tullidinol was detected in the serum of treated animals and that the methods we used for its detection may also help to diagnose accidental tullidora poisoning in cattle and human beings.