The kinetic profile of cytokine gene expression in normal human peripheral mononuclear cells (MNC) activated by an anti-CD3 monoclonal antibody was studied. The presence or absence of 10 different cytokine mRNA were measured in a polymerase chain reaction (PCR) assisted mRNA amplification assay. After 2 h of stimulation the mRNA for interleukin-1alpha (IL-1alpha), interleukin-2 (IL-2), interleukin-3 (IL-3), tumour necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) were detectable and remained present during the whole time period studied (22 h). Interleukin-6 (IL-6) and granulocyte macrophage colony stimulating factor (GM-CSF) were detected after 4 h, while interleukin-10 (IL-10) mRNA did not appear until after 7 h; they all remained expressed at 22 h. A transient expression of interleukin-4 (IL-4) mRNA was observed between 4 and 7 h of stimulation. No gene expression of granulocyte colony stimulating factor (G-CSF) was detected at any time. These results show that anti-CD3 stimulation of MNC leads to a rapid sequential induction of different cytokine mRNA, some with a very transient expression.