Cephalosporin antibiotics in which the 7.beta.-acylamido group has the formula ##STR1## (where R.sup.1 is furyl or thienyl and R.sup.2 is C.sub.1-4 alkyl, C.sub.3-7 cycloalkyl, furylmethyl or thienylmethyl) and in which the 3-position substituent is a pyridiniummethyl group wherein the pyridine ring is optionally substituted by carbamoyl, carboxy, carboxymethyl, sulpho or methyl exhibit high antibacterial activity against a broad range of gram-positive and gram-negative organisms, coupled with particularly high stability to .beta.-lactamases produced by various gram-negative organisms and good stability in vivo, particularly to esterases.