Polyion conformation and the distribution of small ions near the polyion have been investigated using Monte Carlo simulations. The systems of interest contained one polyion and its monovalent counterions, and variable amount of a 3:1 salt. With monovalent counterions only, the polyion is strongly extended. As salt is added, the polyion folds, and the most compact and spherical-like structure appears at a three-fold excess of the trivalent counterions. The polyion exerts a strong influence on the nearest-neighbor distance among the trivalent ions, an effect being relevant for energy transfer reactions. (C) 2003 American Institute of Physics.