Freshly defecated unsporulated oocysts of Eimeria piriformis from rabbit were treated with various concentrations (1%, 2.5%, 5%, and 10%) of chromium compounds, potassium dichromate, potassium chromate, chromium oxide and chromium nitrate, to examine their effect on sporulation. The sporulation time of oocysts treated with 1 to 10% K₂Cr₂O₇ was 28 h. However, much longer sporulation times of about 60 h were required for oocysts treated with 2.5% CrO₃ and Cr(NO₃)₃. Moreover, for oocysts treated with distilled water, 1% K₂CrO₄ and 10% K₂CrO₄, the sporulation times required were 216, 156 and 96 h, respectively. Thus, potassium dichromate was found to have higher catalytic activity for the sporulation of E. piriformis oocysts than other chromium compounds.