The bacteriophage T4 regA protein translationally regulates its own synthesis and the synthesis of several other T4 early proteins. In order to study the mechanism of translational regulation, we have purified the regA protein. Initially a mutant protein, incapable of autogenous repression, was placed under lambda PL transcriptional control and amplified to approximately 10% of total cell protein. The membrane-associated mutant protein was extracted with organic solvent mixtures and purified by reverse phase-high performance liquid chromatography. Polyclonal antibodies prepared against the mutant protein were used in Western blot assays to monitor purification of the wild-type protein from T4-infected cells. Phosphocellulose and poly(U)-agarose chromatography were important steps in its purification. The binding properties of regA protein to polyribonucleotides are discussed in relation to the mechanism by which the protein recognizes its mRNA targets.