LD50 determination in toxoplasma gondi infection in balb/c mice , LD50 is a merker of virulence which is reflects degree of microorganism pathogenecity. LD50 of every pathogens to be used should be determined in order to chose an appropiate infective dose of agents under the study. Toxoplasma gondii RH strain has been maintained in the laboratory by serial passage in mice for several years, in…