The prescribing patterns for the cephalosporins and the cost-savings following restriction of cephalothin sodium and approval of cefazolin sodium were studied over a three-year period at a university hospital. The prescribing patterns for cefazolin relative to dose, frequency, duration of therapy and clinical indications were studied for 64 patients during a one-month period. Parenteral cephalosporin use for three years was analyzed to determine comparative use rates and costs. For the most part, cefazolin was used properly during the one-month study. The greatest misuse was as prophylactic therapy in postsurgical patients. The switch from cephalothin to cefazolin resulted in a projected annual savings of $5,500, equal to more than 10% of the hospital's expenditures for parenteral cephalosporins. The prescribed daily dose of cephalosporin dropped by one-third following the formulary change. The decision to use cefazolin as the major parenteral cephalosporin resulted in substantial cost savings.