The pharmacokinetics of drugs, such as immunosuppressants, justify the need of measuring their blood concentrations in order to adjust their dosage. Therapeutic Drug Monitoring (TDM) of ciclosporin, tacrolimus and mycophenolate mofetil has shown its benefit particularly in the management of renal transplantees, in order to prevent graft rejection. When prescribed in autoimmune diseases, their pharmacokinetic variability and the variability of clinical response would justify TDM in practice. TDM may be useful in systemic lupus, for hydroxychloroquine, in order to monitor patient compliance. Despite insufficient data in the literature, for mycophenolate mofetil, TDM would permit to maintain clinical remission in adults and children with lupus nephritis, as well as in mucosal pemphigoid and idiopathic nephrotic syndrome in children. Studies are still necessary to validate the thresholds and TDM conditions. For azathioprine, TPMT phenotyping is recommended before prescription. For methotrexate, tacrolimus and ciclosporin, data are still sparse on the benefit of TDM, although it may improve tolerance to tacrolimus in lupus. Finally, for infliximab, in case of loss of response in maintenance, TDM may be proposed in parallel with detection of anti-drug antibodies.