“…A positive purified protein derivative response seems to be necessary for maximum BCG anti tumour activity [4,6,15], suggesting that its effectiveness might be nonspecific and results from a delayed hyper sensitivity reaction more than from a response against specific tumour antigens [15]. The superiority of instilla tions, particularly in patients presenting bladder irritabil ity symptoms, as well as the presence of inflammatory lesions [1,4,6] seem to indicate that the inflammatory local response is an essential part of the anti-tumour action of BCG and that this activity represents the by product of nonspecific reaction. It is, however, also pos sible that, stimulated by BCG, lymphocytes and macro phages may inhibit the growth of tumour cells by direct contact or by the release of tumouricidal factors [4], Three kinds of BCG strains have been used for the clinical studies mentioned in this article: lyophilized Pas teur strain BCG [1,2,4,10], Institute Armand Frappier [3,5] and Tice strain [6], with apparently similar benefi cai effects.…”