In homogeneous enzyme immunoassay without requirement of separation of free and bound label, the concentration of substances in samples can be detected by measurement of enzyme activity in the mixtures of samples (antigen) and reagents (labeled antigens antibodies, and enzyme substrates). The methods described herein offer the virtues of simplicity and rapidity by use of general-purpose automated clinical analyzer. The concentrations of some drugs, hormones, antibiotics, and very small amount of certain proteins are now detected by the routine examination in these techniques employing commercial diagnostic kits offered by several companies. In this manuscript, we attempted to give an overview of the principle of various methods by use of commercial diagnostic kit applied in routine clinical examinations.