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the metastases; it may cause serious; even fatal, bacteraemic shock and should be compared with other local forms of treatment. More interesting is the apparent benefit gained by distant intracutaneous inoculation, particularly in the inhibition of metastases. Many trials are in progress to determine this point: unfortunately the only large study so far published’6 is invalidated by the selection of controls not comparable for age and with internal inconsistencies relating to the site of the primary. The data for lung carcinoma are more convincing, since the trials have in general been well conducted with proper controls. 17-19 They suggest that B.C.G., intracutaneous or intrapleural, may well prevent the establishment or growth of distant metastases. A similar effect is also suggested by the early but encouraging results of a trial using levamisole in lung carcinoma. 20 These are the forerunners of a tide of immunotherapy trials most of which, including all C. parvum studies and all breast-carcinoma trials, are still too young to be evaluated. How are they to be assessed? It is important to recall that experimental immunotherapy is only successful in circumstances where there is a reasonably strong tumour-associated antigen, a small tumour load (e.g.,