Oil bodies are lipid storage organelles which have been analyzed biochemically due to the economic importance of oil seeds. Although oil bodies are structurally simple, the mechanisms involved in their formation and degradation remain controversial. At present, only two proteins associated with oil bodies have been described, oleosin and caleosin. Oleosin is thought to be important for oil body stabilization in the cytosol, although neither the structure nor the function of oleosin has been fully elucidated. Even less is known about caleosin, which has only recently been described [Chen et al. (1999) Plant Cell Physiol 40: 1079-1086; Naested et al. (2000) Plant Mol Biol 44: 463-476]. Caleosin and caleosin-like proteins are not unique to oil bodies and are associated with an endoplasmatic reticulum subdomain in some cell types. Here we review the synthesis and degradation of oil bodies as they relate to structural and functional aspects of oleosin and caleosin.