Two new members of the rare isoflavan series and two new pterocarpans have been isolated from Lonchocarpus laxiflorus. Physical methods involved in solving the structural problems associated with the penta-substituted ring B of three of these compounds include the study of methoxy-proton shifts and i.r. stretching frequencies. Some possible errors of the method of methoxy-proton shifts are pointed out. Steric factors result in one isoflavan (Ionchocarpan) and its derivatives taking up unusual conformations; this gives rise to misleading o.r.d. curves and is also reflected in the n.m.r. spectra.