The carbapenem-hydrolyzing class A beta-lactamase Sme-1 from Serratia marcescens S6 was expressed in Escherichia coli and purified by ion-exchange chromatography and gel filtration. Crystals of the purified enzyme were obtained by the hanging drop vapor diffusion method using polyethylene glycol 4000 as precipitant. The crystals belong to the monoclinic space group P21 with unit cell parameters a = 81.48 A, b = 51.76 A, c = 71.81 A, alpha = gamma = 90 degrees, and beta = 118.71 degrees. There are two monomers in the asymmetric unit and the calculated Matthew's volume is 2.26 A3/Da. The crystals, which diffract to at least 2.3 A resolution, are suitable for X-ray structure analysis.