AbstractMuch of the advance in the radiotherapy of Hodgkin's disease has resulted from an increased understanding of the progress of the disease. Neither its origin, nor subsequent spread in the early stages are random, and these observations have led to conjectures as to the mode of spread of Hodgkin's disease. Currently there are two main concepts, one advocated by Rosenberg and Kaplan (1966); Kaplan (1970; 1972) and the other by Smithers (1970). Both concepts give rise to predictions about the course of the disease and these are compared with the observed lymph-node involvements. The hypothesis advocated by Smithers (1970) enables calculations to be made forecasting the complete pattern of involvement in the major lymphnode regions. It is shown that such discrepancies which do arise between the predicted pattern and the observed pattern of involvement are accounted for if allowance is made for secondary influences, such as preferential spread in the direction of lymph flow or distance between sites of involvement, which perturb the pattern predicted solely from the relative susceptibilities of the involved sites.