Most studies of the induction of cytokine synthesis in monocytes have used an exogenous triggering agent such as Lipolpoysaccharide (LPS). However, during nonseptic chronic inflammatory responses (e.g., rheumatoid arthritis) monocyte activation occurs as a result of T cell generated signals. This report demonstrated that plasma membranes from anti-CD3 activated peripheral CD4$\sp{+}$ T cells (Tm$\sp{\rm A}$) but not from resting CD4$\sp{+}$ cells (Tm$\sp{\rm R}$) induced monocytes to synthesize IL-1 in the absence of costimulatory cytokines. The expression kinetics of the molecule(s) unique to activated T cells which interact with monocyte receptors to induce IL-1 demonstrated that optimal expression occurred at 6h post activation. This matched Lederman's, et al., (1992) previously reported kinetics of expression of CD40 ligand (CD40L) on activated peripheral T cells, implicating the CD40-CD40L interaction as a candidate for the initiator of IL-1 induction in monocytes. In this work, it was demonstrated that the signal could be reduced up to 85% by addition of 5c8, a monoclonal anti-CD40L antibody. In addition, a monoclonal anti-CD40 IgM (BL-C4) induced resting monocytes to synthesize IL-1. Experiments demonstrated that crosslinking the CD40 molecules on monocytes was critical for IL-1 induction. Tm$\sp{\rm A}$ but not Tm$\sp{\rm R}$ also up-regulated cell surface expression of adhesion/costimulatory molecules on monocytes including CD40, ICAM-1, and LFA-3. Anti-CD40 signaling up-regulated expression of ICAM-1 and LFA-3. Experiments suggested that signaling through CD40 may utilize a protein tyrosine kinase (PTK) mediated pathway but not a protein kinase C mediated pathway and studies using THP-1, a premonocytic cell line, indicated that the transcription factor, NF-$\kappa$B, was activated through anti-CD40 signaling. Since CD40 ligand-transfected cells alone did not induce IL-1 but Tm$\sp{\rm A}$ did, it was considered that an additional costimulatory cell surface molecule was required. Preliminary experiments suggested that CD69 may be required. In summary, these results indicate that contact-dependent T cell-monocyte interactions, alone, can activate inflammatory cytokine production by resting monocytes and that a critical component of this interaction is the CD40-CD40L signaling event.