A sandwich enzyme immunoassay for collagenase inhibitor was set up with a pair of monoclonal antibodies prepared against bovine dental pulp collagenase inhibitor. Two different combinations of the antibodies were found to be applicable to the immunoassay; one was for the determination of both bovine and human collagenase inhibitors, but the other was only for the bovine one. Minimum sensitivity was 1 pg/tube (3 pg/ml) for bovine collagenase inhibitor and 1.5 pg/tube (5 pg/ml) for human inhibitor. The levels of collagenase inhibitor in several normal human body fluids were measured by the immunoassay, and the values obtained were as follows: serum, 183 +/- 30 ng/ml (mean +/- SD); platelet-poor plasma, 68 +/- 13; cerebrospinal fluid, 60 +/- 13; amniotic fluid, 1,780 +/- 969; tear fluid, 418 +/- 145; mixed saliva, 316 +/- 166; urine, 7 +/- 8.