We have reported the isolation of a number of alkaloids, including three reduced proaporphines (Base E acetate (1), linearisine (2), and jacularine (3)), from Croton linearis. We now describe work establishing the structure of a fourth reduced proaporphine, jaculadine (4), from this plant: isolation involved countercurrent distribution and preparative t.l.c., structural work was carried out on its N,O,O-triacetyl derivative (5), and hydrogenation of this acetate yielded a product identical to deoxyhexahydro-NO-diacetylcrotonosine (6) (prepared by reduction of NO-diacetyltetrahydrocrotonosine (7) from crotonosine (3)), correlating jaculadine with this compound; the configuration at C-6a was assigned based on the sign of rotation similarity. From Croton discolor Willd., we isolated known alkaloids (crotonosine (8), 3,14-dihydrosalutaridine (9), L-N-methylcrotonosine (10), linearisine (2)) and a new minor alkaloid discolorine (11); partial structure of discolorine was established: it has a phenolic group (methylated to an O-methyl derivative dissimilar to amuroline (12), oxidation of which gave a product identical to amuronine (13)), and its mass spectrum showed characteristic fragments. Although reduced proaporphine alkaloids are generally believed to be biosynthesized from proaporphines by enzymatically controlled reduction processes, experiments are being undertaken to ascertain whether the process is reversible in some Croton species containing both types of compounds.