This product contains an L-erythro-sphingosine containing an acetic amide linkage and is useful for comparison studies against the natural D-erythro isomer. This product is also very useful as an internal standard1,2 and contains a short-chain fatty acid enabling it to enter easily into cells. L-erythro-Sphingosine is an inactive or less active isomer of the naturally occurring D-erythro-sphingosine. Natural sphingosine induces dephosphorylation of retinoblastoma gene product and inhibits cell growth while L-erythro-sphingosine is 5-8-fold less active. However, the L-erythro-sphingosine is taken up by cells to the same extent as the natural sphingosine indicating that cellular uptake was not the factor influencing activity.3 L-erythrosphingosine, along with other sphingosine isomers, has been found to be an activator of 3-Phosphoinositide-dependent kinase 1.