During the nineteen sixties, the biosynthetic pathways to the indole and Ipecac alkaloids were largely elucidated by the efforts of several research groups. The non-tryptamine portion of the indole alkaloids was found to be derived from mevalonate (1) via geraniol (2) and nerol (4) which after hydroxylation to (3) and (5) yielded deoxyloganin (6) and subsequently loganin (7). A fascinating cleavage step then generated secologanin (8) which with tryptamine gave rise to strictosidine (9) together with vincoside (10). Our early tracer studies with a mixture of the basic glucosides (9) and (10) established that one or both could be specifically incorporated by Catharanthus roseus (vincarosea) plants into representatives of the three major indole alkaloid families, viz. ajmalicine (11), vindoline (12) and catharanthine (13). Feedings of the separated [O-methyl-3H]bases (9) and (10) to the plants led to the conclusion that 3β-isomer (10) was on the biosynthetic pathway to the alkaloids rather than the 3α-isomer (9) and other workers also found no appreciable incorporation of labelled (9) into indole alkaloids when it was administered to C. roseus plants. However, the lack of match between the configuration at C-3 of (10) and the corresponding site of ajmalicine (11) remained as an incongruous spot on the large biosynthetic canvas. Recent experiments confirmed the foregoing double-labelling results and, satisfyingly, the 3α-isomer (9) was found to be incorporated into the alkaloids. However, (9) was again not incorporated under certain feeding conditions due to degradation of the precursor by non-specific glucosides and this is almost certainly one of the factors in the variable incorporation results observed in the basic glucoside area. We have therefore re-examined this stereochemical point using samples of (9) & (10) synthesised from [m-3H]tryptamine and secologanin (8), taking advantage of the advances in fractionation methods over the past 10 years. The results confirm that the 3α-isomer was incorporated, rather than the 3β (10) and additional confirmation has been adduced. In the Ipecac series, the earlier work had largely defined the pathway and it followed the same track as for the indole alkaloids up to secologanin (8). This then condensed with dopamine, rather than with tryptamine, to form desacetylisoipecoside (14) and desacetylipecoside (15). Fresh syntheses of these two glucosides have been carried out using [1-14C]dopamine and secologanin (8) and the separated products were fed individually to Cephaelis ipecacuanha plants. The results clearly show that the 3α-isomer, desacetylisoipecoside (14) is the precursor of cephaeline (17) and emetine (18), not the 3β-isomer. The 3α configuration of desacetylisoipecoside (14) matches that of the corresponding centre (C-11b) of cephaeline (17) and emetine (18) and so here too the biosynthetic relationship is now stereochemically unexceptional.