We studied in vitro the effects of three ACE inhibitors at therapeutic concentrations on iron-caused alteration of deformability of red blood cells (RBCs). Ramipril and fosinopril act as pro-drugs; their active metabolites are ramiprilat and fosinoprilat. In our study, we used captopril, ramiprilat and fosinoprilat. Chromatographic migration of RBCs (a marker of their deformability) was measured with and without pre-treatment with captopril, ramiprilat and fosinoprilat. The experiments showed that they all suppressed iron caused alteration of RBCs deformability already at therapeutic concentrations. The efficiency of the substances used was dependent on iron concentration.