The depletion of sulphadimidine(SDM) and its N4‐acetyl and hydroxy metabolites was studied in eggs laid by hens after administration of either a single or multiple oral dosages of 100 mg SDM/kg. During medication and until I day after the last dose, the SDM and its metabolite concentrations in the egg white exceeded those in the egg yolk and reflected the plasma levels. In the period starting 2 days after the (last) dosage, the SDM concentration in the yolk became higher than in the egg white, and the drug depletion curves ran parallel. The mean maximum amount of SDM found in the whole egg was 1500 μg after a single and 1280 pg after multiple dosage. In eggs, traces of the N4‐acetyl and 6‐methylhydroxy metabolites could be detected (mainly in the egg white), and their concentrations were approximately 40 times lower than those of the parent drug. A highly significant correlation (P< 0.005) was found between the development stage of the oöcyte at the time of (last) medication and the amount of SDM found in the egg that developed from it. A period of 7 or 8 days after the (last) dosage of 100 mg SDM/kg/day is required to obtain SDM levels below 0.1 μg/g egg.