Approximately 20% of plant species contain alkaloids with a broad range of physiological properties that protect them from various types of herbivores and pathogens. Within this abundant group of nitrogen-containing secondary metabolites, the monoterpenoid indole alkaloids (MIAs) make up the largest and most diverse class of compounds that are characteristically found within the Apocynaceae, Loganiaceae and Rubiaceae plant families. The complexity of MIA chemistry is matched by their remarkably diverse effects on living organisms which has led to their use as drugs for treating neurological disorders (reserpine), cancer (camptothecin, vinblastine and vincristine) and as vasodilators (yohimbine) in humans. Serpentine has recently been shown to be a powerful acetylcholinesterase inhibitor with potential use for treatment of Alzheimer's disease (Pereira et al., 2010). Catharanthus roseus is the best characterised MIA-producing plant, mostly due to the commercial value of its anticancer alkaloids, vinblastine and vincristine. Several recent reviews have been published on the analysis (Hisiger and Jolicoeur, 2007), chemistry (O'Connor and Maresh, 2006), biosynthesis (Facchini and De Luca, 2008; Oudin et al., 2007a; El-Sayed and Verpoorte, 2007; Loyola-Vargas et al., 2007; Hedhili et al., 2007), regulation (Memelink and Gantet, 2007; Memelink, 2009), intracellular, intercellular and organ-specific compartmentation (Mahroug et al., 2007), plant cell culture-based production (Zhao and Verpoorte, 2007), biotechnological production (Zarate and Verpoorte, 2007; Zhou et al., 2009), functional genomics (Goossens and Rischer, 2007) and transport (Roytrakul and Verpoorte, 2007) of MIAs in Catharanthus. Although there have been fewer investigations, studies with Rauvolfia serpentina (ajmaline and reserpine) (Stockigt et al., 2007), Camptotheca acuminata (camptothecin) (Lorence and Nessler, 2004; Sirikantaramas et al., 2007) and Ophiorrhiza pumila (camptothecin) (Sirikantaramas et al., 2007) have also contributed significantly to our biochemical and molecular knowledge of MIA biosynthesis. This review describes some of the significant discoveries with Catharanthus roseus, Rauvolfia serpentina, Camptotheca acuminata and Ophiorrhiza pumila that have helped to highlight information on MIA biosynthesis, its regulation during plant growth and development, the contributions of multiple cell types to different sections of this complex pathway, and the involvement of different intracellular compartments in biosynthesis in the whole plant and/or in cell cultures.