A time course study was performed to reveal the sequence of histopathology after Trichinella spiralis or T. pseudospiralis infection in mice. A cyst was formed in the former case by about 18 days post infection and prominent myopathy was restricted within the cyst. In the latter case, however, no typical cyst was formed, and myopathy spread diffusely over the infected muscle tissues occupying half the area of muscle sections. An electron microscope observation revealed that the disintegration of muscle cells was delayed in T. pseudospiralis infection than in T. spiralis infection. Quantitative reverse transcription polymerase chain reaction (RT-PCR) showed that apoptosis-related genes were expressed for a longer term in muscles infected with T. pseudospiralis than in those with T. spiralis, although the same spectrum of genes are mobilized. Examined apoptosis-related genes included tumor suppressor genes p53, p53; mouse double minute 2, MDM2; cyclin-dependent kinase inhibitor p21 (WAF1), p21(waf) ; Bcl-2 associated protein X, BAX; apoptotic protease activating factor 1, Apaf-1; Caspase 9 and serine/ threonine protein kinase, PKB. Micro-dissection of the infected muscle tissue and subsequent RT-PCR confirmed that the expressions of these genes are restricted to tissue with myopathy. Thus, the expression of the apoptosis-related genes correlated with continuous and diffuse myopathy caused by T. pseudospiralis infection.