Horse radish peroxidase, alkaline phaosphatase and beta-D-galactosidase are widely used as labels in the development of enzyme immunoassays (EIAs). Enzyme beta-lactamase, though introduced as a label in late seventies has not yet become very popular inspite of having the necessary features of an enzyme to be used in EIAs. The present article reviews assays developed with this enzyme, highlights its salient features and brings out an argument in favour of its wide spread use in EIAs.