Meibomian gland disease--and, in particular, obstructive meibomian gland disease--makes an important contribution to ocular surface disease, in the form of meibomian keratoconjunctivitis. With improved methods for the study of meibomian oil composition and function, we are moving closer to the possibility of distinguishing the contribution of meibomian deficiency, as opposed to inflammatory events, to this disorder. More importantly, where aqueous tear deficiency and meibomian gland disease coincide in patients with dry eye, we are closer to the possibility of distinguishing their relative contributions to the dry eye state. This has implications for future therapies.