Thorough large scale investigations of Penstemon secundiflorus ssp. lavendulus and of P. grandiflorus resulted in the isolation of the new iridoid glucosides 5, 6 beta-dihydroxyadoxoside. The structure of 10-hydroxyepihastatoside has been revised to 10-hydroxyhastatoside: using a chemical correlation. Also, the known iridoids (5 alpha H)-6-epidihydrocornin, cornin, hastatoside, 8-epihastatoside, beta-dihydrohastatoside, penstemoside, (5 alpha H)-10-hydroxy-6-epidihydrocornin, 10-hydroxycornin and catalpol were isolated. (C) 1998 Elsevier Science Ltd. All rights reserved.