Characteristic features of the positron binding structure of the urea and acetone molecules are discussed based on the results obtained by the configuration interaction scheme of quantum chemical molecular orbital calculations. This method takes the positron-electron correlation contribution into account explicitly. We have found that the positron distribution is concentrated behind the carbonyl oxygen atom. The positron affinity of urea is larger than that of acetone, which is consistent with the stronger dipole moment of urea. (C) 2003 American Institute of Physics.