Subcutaneous Carcinogenesis by 14 C and 3 H Labelled Polymethylmetacrylate Films *

¹⁴C and ³H labelled and not labelled polymetylmetacrylate films of various sizes were implanted subcutaneously into Swiss mice. Sizes of 3 mm² and 6 × 12 mm appeared to posses a borderline carcinogenic activity, which was not influenced by the labelling. Similarly, the carcinogenic activity of the 12 mm² films was not modified by the ¹⁴C or ³H labelling. There was however a notably higher incidence of tumors in a small group of mice implanted with 15 mm² films labelled with ¹⁴C. The rate of excretion of radioactivity in the urine of mice implanted with the labelled films, rose sharply between the 2nd and the 8th week from implantation. It suddenly fell at the 9th week to minimal values. The rise in the excretion rate of radioactivity observed in the first 8 weeks from implantation, has been attributed to the possible presence of residual monomers in the films.