Libraries of random phage-displayed pentadeca- and hexapeptides were screened with the use of four monoclonal antibodies against the human plasma membrane Ca2(+)-ATPase. Bacteriophages specifically binding the antibodies were selected, and the amino acid sequences of the expressed peptides (mimotopes) were determined. Mimotopes for three antibodies (8B8, 2D8, F9) did not correspond to the Ca2(+)-ATPase sequence. Pentadecapeptides for the 7C8 antibodies displayed similarity to the fragment Glu1097-Arg1113 of the Ca2(+)-ATPase calmodulin-binding site. However, these antibodies failed to bind recombinant fragment Leu1069-Leu1220; therefore, the structure of this epitope remains obscure. This work opens a series of studies of the plasma membrane Ca2(+)-ATPase structure by means of monoclonal antibodies and the phage display method.