7-[2-(5-Amino-1,2,4-thiadiazol-3-yl)-2-(substituted)-iminoacetamido]-3-[3-( quaternaryammonio)-1-propen-1-yl]-3-cephem-4-carboxylates of the formula ##STR1## in which R.sup.1 and R.sup.2 are defined herein and --.sup..sym. N.tbd.Q is a quaternary ammonio group as defined herein, and salts, solvates, hydrates and esters thereof, are potent antibacterial agents. Processes for their preparation and intermediates in such processes are described.