The amount and size of particulate contamination in three commercially available cephalosporin injections and a new product, anophilized cephalothin sodium injection, were studied. Particles in reconstituted cephalothin sodium (commercially available and anophilized), cephapirin sodium, and cephradine injections were counted using two methods: (1) modified USP membrane-filtration technique and (2) Elzone computerized particle analyzer. The amount of particulate contamination in the ranges of 10-24 and greater than or equal to 25 microns was determined by both methods. In the 10-24-microns range, the cephalothin, cephapirin, and cephradine products had significantly greater particle counts than the anophilized cephalothin product. The greater than or equal to 25-microns particle counts showed that the cephapirin and cephradine products had particle counts greater than the anophilized cephalothin product, while total particle counts showed the same results as the 10-24-microns particle counts. A comparison of counting methods showed that the only significant difference between the number of particulates obtained using the modified USP and Elzone computer methods was with the cephalothin product. Anophilized cephalothin sodium injection has significantly fewer particles in the size ranges studied. No conclusion could be reached as to the more accurate method for counting particles.