PURPOSE: To determine streptolysin O in a liquid to be determined stably by using a carrier fixed with a steroid compound having a specified structure to be bonded with the streptolysin O in a liquid to be determined.

CONSTITUTION: A steroid compound represented by a specified formula is fixed physically or chemically to a carrier, e.g. a latex particle or a bead. In the formula, R1 represents a substituted/unsubstituted, saturated/unsaturated cholesterol side chain group or coal acid side chain group, R2 represents hydrogen atom or hydroxy group, and the breaking line position represents a saturated or double bond position. The group R1 represents a saturated/unsaturated cholesterol side chain group or coal acid side chain group having one or two double bond substituted/unsubstituted by hydroxy group, lower alkyl group or lower acyl group. When the carrier is caused to react on a solution to be determined containing streptolysin O derived from group A hemolytic streptococci, only the streptolysin O is bonded specifically onto the carrier.