A retrospective study of our 14-yr records on experimental Taenia crassiceps (ORF(fast) line) cysticercosis (n = 1,198) shows that in 16 of 17 different mice strains, female mice are more frequently infected and carry larger individual parasite loads than males. However, sexual differences in parasite loads significantly varies between strains in relation to their different genetic backgrounds (BALB > C57Bl = OTHERS > C3H). The coefficient of variation in all female mice is significantly smaller than that of all males, an indication of males' more potent, but erratically effective, restraint of cysticercus growth. Similar positive growth bias for female mice is shown by other lines of cysticerci, i.e., HYG(slow) and WFU(slow). These results contravene the usual expectation of female hosts being more resistant than males to parasite infections, and they point to the multiple factors that combined determine sex related differences of mice to experimental cysticercosis infection.