Comparisons were made on the catch rate, sizes of blue crabs (Callinectes sapidus), and bycatch taken in Mississippi Sound waters with crab traps equipped with and without a diamondback terrapin (Malaclemys terrapin) excluder device from April through August 1997. The excluder device consisted of welding rods shaped into a 5 X 10 cm rectangle and fitted into the funnel entrances of a common Gulf Coast crab trap. All blue crabs taken were counted, carapace width measured (mm), and sexed. Bycatch was recorded for each sample. A total of 740 blue crabs were captured, 370 in control traps and 370 in excluder traps. No significant difference in mean size (2-tailed t-test) and catch rate (paired t-test) by trap type was observed. The Kolmogorov-Smirnov 2-sample test indicated a significant difference in the size distribution of blue crabs between the 2 trap types. This statistical difference is attributed to the small sample size of blue crabs collected. No diamondback terrapins were captured in this study. Little difference in the bycatch catch rate was observed between the 2 trap types.