An alternative blot assay for the detection of recombinant proteins using enzyme fragment complementation (EFC) was developed.This novel blotting technique provides similar utility to Western blotting without the need for specific antibodies or multiple incubation and wash steps.In EFC, a short peptide (the α fragment or enzyme donor) derived from the N terminus of β-galactosidase (β-gal) can reconstitute enzyme activity in a corresponding deletion mutant of full-length β-gal.Variants of the α fragment optimized for recombinant expression and high complemented enzyme activity have been created and are known as ProLabel (PL).The utility of the EFC blot assay was demonstrated by evaluating its ability to detect recombinant proteins in extracts prepared from CHO cells transfected with a variety of PL-tagged constructs.