New derivatives of 7 beta-[2-(2-aminothiazol-4-yl)acetamido]cephalosporins having amino group at the 2-position of the 7-acyl moiety were synthesized in the hope that they would show improved antibacterial activity. Some of these compounds (XXa, XXd, XVb) showed improved activity against Enterobacter cloacae. Replacement of the annular amino group by a methyl group caused loss of activity.