The n.m.r. data for several derivatives of taxicin-I, particularly for oxonortaxicin-I tetra-acetate, the spectrum of which is considered in some detail, define substantial parts of the structures. Further structural information was obtained from the preparation and examination of 1,2-, 4,5-, and 9,10-seco-taxicin-I derivatives, and also from reactions involving the hydrogenolysis of oxygen functions at positions 5 and 10. The conjugated system in the derivative (IX; R = Ac, R′= Me) was reduced stepwise in a way which shows its simple αβ-unsaturated ketone nature; a feature of these experiments was the remarkable light absorption, λmax.ca. 225 mµ, found for the unconjugated olefins (XIII). The results establish for O-cinnamoyltaxicin-I the structure (III; R = R′= H) which differs from a tentative earlier proposal only in the position of the exocyclic methylene group.