Investigations were performed to evaluate dietetic influences on fishy or undesired egg taint. Brown layers were selected from a flock with increased occurrence of unpleasant egg taint and malodorous expiries. The hens (all tainters) were randomised into a control and an experimental group of 10 animals each and fed a commercial standard diet that did not contain known critical feed compounds (rapeseed, fish meal) after microscopical examination and had a normal choline concentration. In one phase of the trial the experimental group was fed with a self-mixed diet without critical compounds and vitamin supplement. In a consecutive feeding trial an oral antibiotic treatment with neomycin and tetracycline or neomycin, metronidazol and enrofloxacin reduced egg taint in the experimental group compared with the control group, while neomycin alone had no significant effects. It can be concluded, that the gram positive gut flora significantly contributes to the formation of undesired odorous substances. Mannose oligosaccharides, lactulose and a herb extract (oregano, thyme) did not have any efficacy against the taint problem. A single procedure may be misleading for the common selection practice against egg taint by testing of the expiries due to the considerable day to day variation. It has also to be questioned, whether ionophores given as coccidiostats during the growth phase reduce egg taint inhibiting effective selection by olfactory tests.