Erythrodiol is the precursor of pentacyclic triterpenic acids present in Olea Europaea. Although olive oil and some of its constituents are reported to have anticarcinogenic activities, erythrodiol has not been assessed in its cell biological functions in detail. We therefore determined its effects on cell growth and apoptosis in human colorectal carcinoma HT-29 cells. Proliferation, cytotoxicity, and apoptosis were measured by fluorescence-based techniques. Erythrodiol inhibited cell growth with an EC50 value of 48.8 +/- 3.7 microM without any cytotoxic effects in a concentration range up to 100 microM. However, exposure of cells for 24 h to 50, 100, and 150 microM erythrodiol increased caspase-3-like activity by 3.2-, 4.8-, and 5.2-fold over that in control cells. We here demonstrate for the first time that, in colon adenocarcinoma cells, erythrodiol exerts antiproliferative and proapoptotic activity.