Abstract: A color changing reagent composition for coating onto syringe needles and other needle containing medical devices which upon contact with such bodily fluids as blood, mucous, saliva, and semen will cause the composition coated needle to change in color to signal a prior use and contamination with a possibly infected bodily fluid. The preferred composition is selected from the group consisting of guaiac acid, benzidine, Barfoeds solution, Benedicts solution, cresol, catechol, phenylenediamine, Haynes solution, phenol, leuco malachite green, leuco-crystal violet, peroxidase, pseudoperoxidase, orthotolodine, orthordianisidine, cumene hydroperoxide, tretramethylbenzedene and 2,2-azinodi-(3-ethylbenzyl)azoline sulfunic acid. After the coated needle comes in contact with a bodily fluid having a catalyst it will, upon oxidation, change from being in a colorless state to having a visually detectable color.