The antitumor and antimetastatic activities of the plant cysteine endoproteinase bromelaine were evaluated in a murine model. Syngeneic sarcoma L-1 cells were incubated with bromelaine (after preceeding time and dosage kinetics) and subcutaneously; (s.c.) or intravenously; (i.v.) inoculated into BALB/c-mice (n = 5 per experimental group) to induce local tumor growth or lung colonization. Compared to non-protease incubated L-1 cells, local tumor growth and experimental lung metastasis decreased significantly (p < 0.05). After bromelaine incubation of the tumor cells. Sarcoma L-1 cells induced local tumor growth after s.c. inoculation and lung colonization after i.v. injection. Intraperitoneal (i.p.) or s.c. administration of bromelaine (optimal dosage and time schedule tested in preceeding kinetic studies) significantly (p < 0.05) reduced local tumor weight, however, lung colonization was non-significantly reduced. Bromelaine incubation of sarcoma L-1 cells significantly reduced their tumorigenic/metastatic capacities. Bromelaine treatment after tumor cell inoculation significantly reduced local tumor growth, experimental lung metastasis, however, to a lesser, non-significant degree.