Microarray technique was employed to study differences in gene expression profile induced by Aplidine treatment in the Molt-4 human leukemic T cell line. Aplidine is a novel marine compound purified from caribbean tunicate (sea squirt) Aplidium Albicans. Despite promising anti-tumor activity, few data are available on its mechanism of action. Exponentially growing cells were treated with Aplidine concentrations close to its 5IC50 for 1 hour and RNA samples collected after 0.5, 1, 6 and 24 hours of recovery in drug free medium. 32P labelled cDNAs were hybridized against Atlas Human Cancer arrays onto which 588 cDNAs were spotted. Genes involved in different cellular pathways, (such as growth factors, signal transduction or transcription factors) were found modulated by the drug. Even if the data obtained in the present study cannot be conclusive, several hypothesis on Aplidine's mechanism of action are indicated that will be the subject of future studies.