SummaryThis review reports recent methods by which organic compounds, and especially pharmaceuticals, have been isotopically labelled by the incorporation of carbon or hydrogen isotopes in methylation processes. Particular attention is paid to the incorporation of carbon-11; both the synthesis of such labelled methylating agents and applications of their use are discussed. The review has reported reagents and conditions by which a number of organic compounds have been obtained recently. It also assesses the limitations of reported methods and proposes some alternative techniques and innovations.The application of catalysts such as Ag + and conditions such as microwave irradiation to encourage these reactions are also included, with suggestions of other, potentially beneficial, ways to assist them. In many cases, the radio-chemical yield and purity of the labelled product are given along with an estimate of the total reaction time.