Catharanthus roseus cell suspension cultures were used to bioconvert both triptolide (1) and triptonide (2). The same reaction path was followed in both biotransformations. Two biotransformed products were obtained and their structures identified as triptriolide (3) and 12beta,13alpha-dihydroxytriptonide (4), respectively, from 1 and 2. Product 4 is a new compound.