Mycobacterium avium subsp. paratuberculosis (MAP) can be present in bulk tank milk at farm level as a consequence of direct excretion of the organism within the udder and/or indirect contamination with infected faeces during the milking process. In-line milk filters are generally sited between the milking equipment and the bulk tank to remove gross foreign material including faeces from the milk. Examination of these milk filters may provide a means of detecting MAP infected milk at farm level. A survey of in-line raw milk filters from dairy farms in Southern Ireland is currently in progress to assess this. To date 122 milk filters have been examined for the presence of MAP. Upon arrival at the laboratory each sample consists of a filter and some transit milk. The filter is removed and homogenised in a stomacher with 100ml Phosphate Buffered Saline containing Tween 20 (0.05%) for 2 min. The homogenised sample is recombined with the transit milk, which is divided into two 50ml portions. One portion is subjected to immunomagnetic separation followed by IS900 PCR (IMS-PCR), the other portion is decontaminated with 0.75% (w/v) hexadecylpyridinium chloride for 5 h before culture on Herrold's egg yolk medium slopes and in BACTEC 12B radiometric medium. Of the 122 in-line milk filters tested, 15 have tested positive for MAP by IMS-PCR and also a number of suspect culture positives have been obtained. An assessment will be made of the feasibility of this method to identify potentially Johne's infected herds.