Trichinella spiralis is a parasitic nematode that infects many mammals, including humans. Hosts may experience significant physiological changes or may die because of acute inflammatory immune responses toward the parasite. In this study, oldfield mice (Peromyscus polionotus) were used as a new experimental host for T. spiralis. Males of P. polionotus were infected with increasing doses of T. spiralis to determine the effect infection had on survival, mass change, total mass, and relative organ masses. Total juvenile worm burden increased in an asymptotic fashion with infective dose. Large doses (≥600 juveniles) significantly reduced survival. There were significant negative correlations between infection intensity (log₁₀[juveniles]/g) and both mass gain and final total mass. Infection had no effect on liver or spleen size. But there were significant negative correlations between T. spiralis intensity and both testis and seminal vesicle masses. These effects on male size and reproductive organs may help explain behavioral changes, such as the elimination of male dominance, seen in previous studies on mice infected with T. spiralis.