Large-scale clinical trials using C(2) monitoring of cyclosporine (CsA) microemulsion (Neoral) in renal transplant recipients have demonstrated low acute rejection rates and good tolerability with a low adverse event profile in a variety of settings: with or without routine induction therapy; in combination with mycophenolate mofetil; with standard-exposure or low-exposure Neoral; and in patients with immediate or delayed graft function. In liver transplantation, C(2) monitoring significantly reduces the severity and incidence of acute rejection compared with C(0) monitoring, without adverse consequences in terms of renal function or tolerability. Different C(2) targets are appropriate depending on adjunctive immune suppression, level of immunologic risk, CsA tolerability, risk of renal toxicity and time since transplantation. CsA absorption may increase substantially in most patients during the first 1-2 weeks post-transplant, and this should be taken into account to avoid overshooting C(2) target range. A patient with a low C(2) value may be either a low or a delayed absorber of CsA, or be a normal absorber who is receiving too low a dose of Neoral. C(2) monitoring alone is insufficient to differentiate between these types of patients, and measurement of additional timepoints is recommended. Adopting C(2) monitoring in maintenance transplant patients identifies those who are overexposed to CsA. In summary, randomized, prospective, multicenter studies and single-center trials have evaluated Neoral C(2) monitoring within a range of regimens in different organ types, providing a robust evidence base for the benefits of this sensitive monitoring technique.