The antiserum against calretinin is produced in rabbits by immunization with recombinant human calretinin containing a 6-his tag at the N-terminal. The antibody was evaluated for specificity and potency: a) by Biotin-Avidin labeling of cryostate-, vibratome- and paraffinsections of 4% paraformaldehyde fixed brains and b) by immunoenzymatic labelling of immunoblots. The product is a polyclonal antiserum against calretinin (1), a calcium-binding protein of the EF-hand family related to calbindin D-28k and calmodulin. The antibody reacts specifically with calretinin in tissue originating from human, monkey, rat, mouse, guinea pig, chicken and fish (Fig. 1). This antiserum does not cross-react with calbindin D-28k or other known calcium binding-proteins, as determined by immunoblots and by its distribution in the brain (Fig. 2).