An increase in attachment of SRBCs to Procambarus clarkii hemocytes has been shown after the crayfish were injected with a live or killed Pseudomonas strain RS2b. The increase in attachment occurred at 8 hours post injection and peaked at 24 hours for both experimental groups. The population of hemocytes with receptors for LPS and mannose also increased at 8 hours post injection and peaked at 24 hours for both experimental groups. At 96 hours post injection the number of receptor bearing hemocytes and hemocytes bound to SRBCs began to decrease to the level of the control for both groups. The protein concentration of hemolymph from the experimental groups remained stable at 8 and 24 hours post injection and increased at 96 hours. The correlation of the protein concentration increase at 96 hours with the decrease of receptor bearing hemocytes may be due to the degranulation of the receptor bearing hemocytes.