Dendritic cells (DC) are central to the control of adaptive immunity. Their ability to activate antigen-specific T cells depends on their maturation state. Many microbial and inflammatory products have stimulated DC maturation. This in vitro study used assays of phenotype and function to examine the potential of bacillus Calmette-Guérin, muramyl dipeptide, and CpG-rich oligodeoxynucleotides to stimulate DC maturation. A chemical fixation method was developed to reliably assess the functional potential of stimulated DC within a mixed lymphocyte reaction model. Using this method, it was shown that bacillus Calmette-Guérin provides a maturation signal as effective as the prototype DC stimulant interleukin-1&bgr;. Furthermore, weaker stimuli such as muramyl dipeptide and CpG-rich oligodeoxynucleotides also are able to induce functional maturation of DC. Using chemical fixation, it was possible to generate stable DC in an immature or a mature state. These observations have importance for our understanding of the regulation of adaptive immunity and for the design of DC-based immunotherapeutic strategies.