The effects of different cation containing products on the absorption of lomefloxacin were evaluated in eight healthy volunteers in a five-way randomized crossover study. The treatments were lomefloxacin alone, lomefloxacin with milk (300 ml), lomefloxacin with calcium carbonate (corresponding to 500 mg calcium), lomefloxacin with ferrous sulfate (corresponding to 100 mg elemental iron), and lomefloxacin with sucralfate (1 gm). Treatments were separated by a 7-day washout period. The bioavailability of lomefloxacin was significantly reduced when it was given with sucralfate; the area under the plasma drug concentration-time curve (AUC) from 0 to 24 hours was reduced by 51% (p < 0.05). Ferrous sulfate reduced the maximum plasma concentration of lomefloxacin by 26% (p < 0.05), the total amount of lomefloxacin recovered in urine by 15% (p < 0.05), and the AUC by 13% (p = 0.26). Calcium carbonate and milk had no significant effects on the bioavailability of lomefloxacin. We conclude that concomitant use of lomefloxacin and sucralfate should be avoided. It may also be advisable not to take lomefloxacin with ferrous sulfate, although this interaction is probably of no clinical significance. Calcium carbonate and milk do not affect lomefloxacin absorption.