Galectin-3 is an animal lectin, formerly named epsilon-binding protein or Mac-2, which has been described to play an important role in some inflammatory processes by the implication of different cells and the increase in cell adhesion functions through laminin binding activity. In this work we analyzed the role of galectin-3 in the modulation of Th2 cytokines that have an important role in the development of the inflammatory response. We have found that the addition of galectin-3 to human eosinophils, the eosinophilic cell line EoL-3, PBMC, and an Ag-specific T cell line (CD4+) produced a selective inhibition of IL-5 transcription. No inhibitory effect was found on the IL-4 mRNA transcription rate. The inhibitory effect on IL-5 transcription was reversed by incubation with lactose and using specific Ab against galectin-3. Galectin-3 is able to induce inhibition of the IL-5 released in the supernatants from PBMC stimulated with phorbol 12,13-dibutyrate and anti-CD3. Similar results were obtained when a T-specific cell line was stimulated with Ag. Also, EoL-3 stimulated with anti-CD32 produced IL-5 protein, the synthesis of which was partially inhibited by galectin-3. The present results demonstrate that galectin-3 induces a selective down-regulation of IL-5 expression in different cell types, opening important new possibilities in the regulation of the allergic reactions.