A total of 14,842 farmed deer were slaughtered and examined postmortem in Irish abattoirs between January 1993 and September 1996. Lymph node lesions were detected in 119 deer and these were examined histopathologically and cultured. A total of 115 of the lesions were characterised as tuberculous and, on culture, Mycobacterium avium was isolated from 49 of them, M bovis from 41, unclassified mycobacteria from five, and 20 of the tuberculous lesions did not yield any isolate. Tubercles which yielded M avium on culture contained on average more acid-fast bacilli, more epithelioid macrophages and fewer Langhans giant cells than tubercles from which M bovis was isolated. Twelve lesions from feral deer culled from a national park were also examined and M bovis was isolated from nine.