Discovery of the growth-link to bradyzoite differentiation—Toxoplasma development follows a pre-determined genetic program.  In 1996, we made the key discovery that T. gondii tachyzoites emergent from a sporozoite infection spontaneously differentiate into bradyzoites.  As they emerge from the sporozoite-infected host cell, VEG strain tachyzoites grow very fast, like the highly virulent RH strain.  At ~20 divisions this growth suddenly slows and the parasites then differentiate.  Whether VEG sporozoites infect an immunocompenent or compromised mouse strain, they develop into bradyzoites in 7 days indicating the course of development is predetermined.  Parasite mutants trapped in the fast growth phase are incapable of differentiating unless they are forced to slow their growth by stress intervention.  These growth mutants are highly virulent---100 % of mice inoculated at doses of <10 mutant parasites die in ten days whereas inoculation of a million wild type VEG tachyzoites into outbred mice is asymptomatic (Jerome et al., 1998, Radke and White, 1999).  The discovery that cell cycle mechanisms are closely linked to parasite development and influence virulence spurred the development of our program on the regulation of Toxoplasma growth.