The identification of protective helminth antigens remains the most important challenge in the development of parasitic vaccines. To identify protective antigens of Ostertagia ostertagi, an important abomasal parasite of cattle, parasite-specific local antibodies from the abomasal mucus and from the draining lymph nodes were collected from calves immunized with multiple infections and from ‘primary infected’ animals. With these probes, Western blots of extracts and excretion/secretion (E/S) material from L3, L4 and adult life-stages as well as cDNA expression libraries were screened to identify antigens that were exclusively recognized by antibodies from ‘immunized’ calves. In the adult stage, a protein of 32 kDa was specifically detected on Western blot by mucus antibodies from ‘immunized’ animals. In the L3 and L4 larval stages, proteins situated in the regions of 28–29 kDa were recognized by mucus antibodies and a 59 kDa antigen was specifically recognized by lymph node antibodies from ‘immunized’ animals. Screening E/S material revealed no specific difference in recognition pattern between ‘immunized’ and ‘primary infected’ animals. Screening of the cDNA libraries revealed 26 relevant clones, coding for 15 proteins, among these several with potential protective capacity, immunodominant properties or functional and physiological importance e.g. metalloproteases, an aspartyl protease inhibitor and collagen.