The isolation and sepn. of the mol. variants of monoclonal IgA from cell culture supernatants is possible using several filtration and ion-exchange chromatog. steps, followed by size-exclusion chromatog. for the actual sepn. of the mol. variants. The latter step is esp. time consuming and laborious. This report presents possible improvements of the procedure. Use of the displacement rather than the elution mode may render the ion-exchange step more productive (higher product concns. and space-time yield). For the final sepn. of the mol. variants, hydroxyapatite (HA) elution chromatog. can serve as an alternative to size-exclusion chromatog. By using an optimized, complex phosphate gradient, the IgA dimers can be sepd. quant. from the monomers and higher oligomers. It may in individual cases be necessary to use a size-exclusion polishing step to reach the required final degree of purity, however, the amt. of material to be processed is reduced to such an extend by the HA-step, that the overall process is still more productive. Buffer pH and flow-rate as well as the stationary phase material used were addnl. factors considered during the optimization of the HA elution chromatog. HA-displacement chromatog. resulted only in a concn. of the overall IgA fraction, but not in a sepn. of the mol. forms. [on SciFinder (R)]