The present invention provides novel 2.alpha.-methyl-2.beta.-[(1,2,3-triazol-1-yl)methyl]penam-3.alpha.-carbox- ylic acid benzhydryl ester (TMPB)-acetone crystals for use in the production of 2.alpha.-methyl-2.beta.-[(1,2,3-triazol-1-yl)methyl]penam-3.alpha.-carbox- ylic acid 1,1-dioxide benzhydryl ester (TAZB); a process for producing the TMPB-acetone crystals comprising the steps of (A) concentrating a TMPB-containing organic solvent solution, (B) dissolving the resulting concentrate in acetone, and (C) precipitating TMPB-acetone crystals from the acetone solution thus obtained; and a process for producing TAZB comprising the step of reacting the TMPB-acetone crystals with an oxidizing agent.