Social desirability and intellectual limitations were investigated as possible determinants of two response biases--acquiescence and naysaying--among mentally retarded respondents. Results clearly indicated that naysaying and acquiescence occur more frequently among lower IQ individuals and naysaying occurs more frequently concerning prohibited behavior, whereas respondents acquiesce regarding desirable behavior. These results suggest that intellectual limitations predispose people to biased responding, whereas social desirability factors determine the type of bias.