Enterally absorbable diastereomers of 1-(isopropoxycarbonyloxy)ethyl (6R, 7R)-7-[2-(2-aminothiazol-4-yl)-2-(Z)-(methoxyimino)acetamido]-3-(methoxymethyl)-3-cephem-4-carboxylate of the formula I ##STR1## and their physiologically acceptable salts and also diastereomerically pure salts of the compounds of the formula II ##STR2## where HX is a mono- or polybasic acid and where X is an inorganic or organic physiologically acceptable anion, and a process for the preparation of these compounds of the formula I or II, which comprises first precipitating the more sparingly soluble diastereomer of the formula IV in the mixing together of 1 equivalent of a solution of the diastereomer mixture of the formula III with 0.2-2 equivalents of a solution of the acid component HY and separating it off by filtration, then precipitating the more readily soluble diastereomer of the formula IV from the filtration solution, it being possible for the acid component HY to be identical or different in the consecutive steps.