The objective of the study was to determine if the adhesion of E. coli K88 to piglet intestinal mucus could be inhibited in vitro by spray-dried egg-yolk anti-K88 antibodies. Binding of E. coli was monitored using a radioactive assay. Four 14+/-2-day-old healthy piglets were used for the preparation of mucus from the small intestine. Competition and displacement phenomena were investigated by incubating (a) egg-yolk antibodies and E. coli together prior to adding to the mucus and (b) E. coli and mucus, followed by egg-yolk antibodies. The results demonstrated that egg-yolk antibodies inhibited the adhesion of 3H-labeled local strain of hemolytic E. coli K88+ (E. coli K88+ MB) to piglet small intestinal mucus by 84.6-97.0% when the egg-yolk antibodies were diluted 10, 20, 40 or 100 times. The adhesion inhibiting effects of egg-yolk antibodies declined dramatically when the antibody dilution was more than 250-fold. A similar adhesion inhibiting effect was observed when egg-yolk antibodies were incubated with E. coli K88+ MB for 15, 30 and 60 min prior to the adhesion test. Egg-yolk antibodies when diluted 50- and 100-fold had a very strong inhibiting ability against E. coli K88+ MB at a concentration of 10(9) colony forming units (cfu) ml(-1) (adhesion was < 6%). However, dilution of 100 times for egg yolk antibodies was insufficient to inhibit the adhesion of E. coli K88+ MB to intestinal mucus when the concentration of E. coli K88+ MB was 10(10) cfu ml(-1). The displacement test indicated that there was no significant reduction in the adhesion of E. coli K88+ MB to the small intestinal mucus when egg-yolk antibodies were added after adhesion of the organism to the mucus. These studies demonstrate that anti-K88+ MB fimbriae antibodies from chicken egg-yolk when added to E. coli K88+ MB prevented their binding to receptors in the mucus isolated from the intestine of piglets.