We recently showed that, in our Trichinella spiralis rat model, first exposure, but not re-exposure to infective-stage larvae evoked heat shock responses in 4 test organs. Our work, however, failed to implicate either early complete clearance of challenge muscle larvae (ML), or rapid elimination of newborn larvae (NBL) in the phenomenon noted in reinfected rats. This study clarifies that issue using 2 established facts in T. spiralis biology and anti-T. spiralis immunology. That is, adult worms injure gut cells and immune destruction of NBL requires release of material also toxic to host cells. To approach the above problem we analysed relevant and irrelevant rat organs for increased heat shock protein (HSP) production at 1, 7, 14, 20 and 27 p.i. during first and second infections. Organs examined were intestines, mesenteric lymph nodes (MLN), heart and lungs. Using densitometric analyses of immunoblots, increased HSP expression was detected on day 7 in intestines from both primary and secondary-infected rats albeit that the change in the latter was just short of significant. Interestingly, MLN only exhibited increased HSP levels in the reinfected rat model with increased HSP levels persisting for 1 week. A lasting shock response was detected in reinfected rats; in contrast, first exposure resulted in shock responses being evident in lungs at either day 7 or day 14, only. These findings suggest that (i) in immune rats, a few challenge ML develop into adults, produce NBLwhich are trapped within MLN, and (ii) that anti-T. spiralis and/or anti-NBL immunity is associated with an, as yet, uncomprehended stress to host's heart tissues.