Procambarus clarkii hemocytes have been shown to bind to both LPS and a mannose containing neoglycoprotein conjugated to fluorescent probes. A decrease in the observed number of fluorescent hemocytes indirectly indicated that the binding of FITC-LPS to these cells is impaired by initial incubation with LPS. Prior treatment of hemocytes with horseradish peroxidase, a mannose rich glycoprotein, decreased their capacity to bind mannose. Mannan had no inhibitory effect on the binding of either ligand. Mixed hemocytes and hemocyte subpopulations separated by buoyant density were incubated with both ligands and revealed that a subpopulation of granular hemocytes bound both LPS and mannose. These results suggest the possible presence of two different pattern recognition cell surface receptors on this subpopulation of granular hemocytes from the red swamp crayfish, Procambarus clarkii, which may specifically recognize and bind to both LPS from gram-negative bacteria and to mannose containing glycoproteins found on microbial surfaces.