OBJECTIVE To investigate the effect of excretory/secretory proteins from Trichinella spiralis on apoptosis of NCI-H446 small-cell lung cancer cells. METHODS Trichinella spiralis muscle stage larvae (5 x 10(6)/ml) were cultured in culture media for 24 h, the excretory/secretory proteins were collected from the supernatant of culture media. NCI-H446 small-cell lung cancer cells (No. A05) were randomly divided into three groups: experiment group (A), standard control group (apoptosis group, B), and control group (C). NCI-H446 cells in groups A and B were cultured with 0.3 mg/ml T. spiralis excretory/secretory proteins, and 6.4 microg/ml cisplatin for 24 h, respectively. NCI-H446 cells of group C were cultured for 24 h without any treatment. The expression of Bcl-2, Fas and Fasl mRNA was detected by RT-PCR. C-myc protein expression level was examined by Western blotting and immunofluorescence assay. RESULTS The level of Bcl-2 mRNA was lowest in group A(0.575 +/- 0.047) , Bcl-2 mRNA level in group C (0.975 +/- 0.069) was higher than that of group B (0.850 +/- 0.073) (P<0.05). Fas mRNA level was highest in group A (0.975 +/- 0.115), followed by group B (0.817 +/- 0.121) and group C(0.769 +/- 0.061) (P<0.05). The level of Fasl mRNA in groups A, B, and C was 0.669 +/- 0.051, 0.787 +/- 0.124, and 0.875 +/- 0.125, respectively (P<0.05). Fas/Fasl mRNA ratio in groups A, B, and C was 1.475, 1.038, and 0.878. Western blotting showed that the expression of C-myc protein in group C (1.172 +/- 0.026) was highest, followed by group B (1.074 +/- 0.069) and A (0.566 +/- 0.054) (P<0.05). Immunofluorescence test indicated that the C-mye protein was found in the cytoplasm and the nucleus 24 h after treated with 0.3 mg/ml T. spiralis excretory/secretory proteins and 6.4 p.g/ml cisplatin. CONCLUSIONS Trichinella spiralis excretory/secretory proteins may inhibit apoptosis of NCI-H446 small-cell lung cancer cells by reducing the apoptosis protein C-myc and Bcl-2 mRNA levels, and causing the increase of Fas/Fasl mRNA ratio.