This review presents and explores the hypothesis that N-arachidonoylethanolamine (AEA, also called anandamide) is transported across cellular membranes by a process that is protein-mediated. Support for this hypothesis comes from experiments demonstrating that cellular accumulation of extracellularly applied AEA is saturable, time and temperature dependent and exhibits selective inhibition by various structural analogs of AEA. The accumulation of AEA is cell specific; data is presented demonstrating that several cell types, including the bovine adrenal zona glomerulosa cell, exhibit very high capacity for AEA accumulation while others, such as the HeLa cell, have a very low capacity. The transport process has the characteristics of facilitated diffusion; it is bi-directional, not dependent on either ATP or extracellular sodium and exhibits the trans effect of flux coupling. Several important questions remain to be answered regarding the carrier, including its molecular structure and its role in the release and inactivation of endogenously produced AEA.