Activated T cells induce contact-dependent chemokine production by human macrophages. Lymphocytes were left unstimulated or were stimulated with either anti-CD3 for 48 hours (Ttcr cells) or a 'cocktail' of inflammatory cytokines (tumour necrosis factor alpha (TNFα), IL-2, IL-6) (Tck cells) for 8 days, before fixation. The unstimulated, Ttcr and Tck populations were then cultured with macrophage-colony stimulating factor-differentiated monocytes (ratio 7:1) for 18 hours. Culture supernatants were then isolated and levels of CC chemokines (monocyte chemoattractant protein 1 (MCP-1), macrophage inflammatory protein 1 alpha (MIP-1α), macrophage inflammatory protein 1 beta (MIP-1β), RANTES) and CXC chemokines (IL-8, growth-related gene product alpha (GROα) and interferon-gamma-inducible protein (IP-10)) measured by ELISA. In some cases, a porous membrane insert was used to physically separate the two populations, while allowing the transition of soluble mediators. Results are shown from (a) Ttcr-cell lymphocyte cultures and (b) Tck-cell lymphocyte cultures. Data represent a mean of triplicate cultures ± standard deviation and are representative of at least three experiments. Statistically significant differences in chemokine detection are indicated.