Preparations of lipoteichoic acid (LTA) from strains of streptococci and lactobacilli were examined for their ability to stimulate the release of enzymes from rat peritoneal macrophages in vitro. The three lysosomal enzymes, acid phosphatase, N‐acetyl‐β‐D‐glucosamini‐dase and β‐galactosidase, were detected but not collagenase. Generally, the secretion of the lysosomal enzymes was not inhibited by cychloheximide, indicating that only preformed enzyme was being released. In contrast, cycloheximide partially inhibited the release of lysosomal enzymes by lipopolysaccharides (LPS).

Summary.-The subcutaneous growth of 2 antigenically distinct syngeneic methylcholanthrene-induced murine fibrosarcomas, designated HI and H7, were significantly augmented by the concomitant administration of E. coli endotoxin (LPS).Amounts as little as 0*02 ,-g i.p. potentiated tumour growth. The weakly antigenic tumour, Hi, was more susceptible to provocation by LPS than the more strongly antigenic H7. Maximum provocation of HI tumour growth occurred when LPS was injected 1 day before the administration of 5000 tumour cells. In contrast, significant anti-tumour resistance resulted if LPS was administered 6 days before the inoculation of tumour cells. Preliminary evidence indicates that low doses of LPS can facilitate the "sneaking through" phenomenon. Enhancement of tumour growth could not be demonstrated with sera or plasma from tumour-bearing mice, unless the samples were contaminated with endotoxin. The results illustrate the importance of excluding endotoxin from solutions used in studies of experimental tumours.

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Tritium-labelled lipoteichoic acid ('H-LTA) was examined for its interaction with connective tissue components by employing autoradiography. Evidence was obtained for LTA binding to both the calcified matrix and to cells of neonatal rat parietal and long bones in vitro. The interaction of LTA with bone-derived cells was studied in a model system utilizing an osteosarcoma cell line in tissue culture. These tumour cells incorporated *H-LTA as long as they were actively dividing but deacylated LTA was not incorporated. This suggested that the lipid portion of the molecule was necessary for interaction with the cells. Evidence has also been obtained for an interaction of LTA with components from the culture fluid of osteosarcoma cells.