Parenteral formulations of rapamycin 42-ester with 3-hydroxy-2-(hydroxymethyl) -2-methylpropionic acid (CCI-779) are provided. One parenteral formulation contains CCI-779, an alcoholic co-solvent, and an antioxidant. Another parenteral formulation contains CCI-779, an alcoholic solvent, an antioxidant, a diluent solvent, and a surfactant. Processes for preparing parenteral CCI-779 formulations using a co-solvent concentrate are also provided.