The effect of beta-endorphin (beta-END) stimulation of cytokines production by PHA-induced human peripheral blood mononuclear cells (PBMC) was studied by reverse transcription in combination with polymerase chain reaction (RT/PCR), slot blotting and hybridization to detect and measure messenger RNA (mRNA). beta-END significantly and dose dependently enhanced IFN-gamma and IL-2 mRNA expression of T cells and naloxone (Nal) reversed the effect of beta-END on IL-2 mRNA expression. The results further demonstrate the important link between the neural system and the immune system.