The discovery of carboxylic acid metabolites of the cannabinoids (CBs) dates back more than three decades. Their lack of psychotropic activity was noted early on, and this resulted in a total absence of further research on their possible role in the actions of the CBs. More recent studies have revealed that the acids possess both analgesic and anti-inflammatory properties and may contribute to the actions of the parent drug. A synthetic analog showed similar actions at considerably lower doses. In this review, a brief survey of the extensive literature on metabolism of delta 9-tetrahydrocannabinol to the acids is presented, while more emphasis is given to the recent findings on the biological actions of this class of CBs. A possible mechanism involving effects on eicosanoids for some of these actions is also suggested. Finally, an analogy with a putative metabolite of anandamide, an endogenous CB, is discussed.