OBJECTIVE Omalizumab, a subcutaneously administered anti-IgE antibody, is effective for moderate-to-severe persistent allergic asthma. The aims were to (i) describe the population pharmacodynamics of free IgE with a mechanism-based, nonlinear, omalizumab-IgE binding model; (ii) deduce a target-free IgE suppression level by correlation with clinical outcomes; and (iii) check the adequacy of current approved dosing tables and explore potential doses and regimens beyond. METHODS Concentration data (omalizumab, free and total IgE) were obtained from 1781 patients aged 12-79 years, in four sparsely sampled randomized, placebo-controlled studies and 152 subjects in a richly sampled single-dose study. NONMEM predictive performance across the range of bodyweights (39-150 kg) and baseline IgE (19-1055 IU ml(-1)) was checked by simulation. Predicted free IgE levels were correlated with time-averaged patient diary clinical outcomes. RESULTS The model accurately predicted observed omalizumab, free and total IgE concentrations. Free IgE concentrations correlated well with clinical signs and symptoms, allowing a target concentration of 14 ng ml(-1), at the midpoint of 4-week clinical observation periods, to be set for determining the dose and regimen for omalizumab. CONCLUSIONS The omalizumab-IgE binding model is predictive for free IgE and demonstrates a nonlinear time-dependent relationship between free IgE suppression and clinical outcomes in asthma. Although currently approved dosing tables are close to optimal, it should be possible to treat patients with higher levels of baseline IgE if higher doses can be administered.