The detection of small concentrations of N-nitrosamines in biological materials requires their prior selective extraction and concentration. A procedure is described for the separation of both volatile and non-volatile N-nitrosamines as a class, and their subsequent determination at low levels. N-Nitrosamines are adsorbed from aqueous solution on to activated carbon from which many can be desorbed to varying extents by refluxing with methanol. Two sensitive techniques are used for the determination of separated N-nitrosamines, namely differential polarography at acid pH and the release of nitrite on ultraviolet irradiation at alkaline pH in the manner of Daiber and Preussmann. The properties of N-nitrosamines and related compounds are compared and methods of differentiating between the groups of compounds are discussed.