ABSTRACT A mycobacterial restriction fragment length polymorphism probe, pUCD, has recently been described which represents an effective tool for the strain typing of Mycobacterium bovis . The present study evaluated this probe, in combination with the direct repeat probe (DR), for the molecular typing of 90 strains of Mycobacterium tuberculosis from 87 patients, looking at a group (62 isolates) of nonselected samples to assess pUCD combined with DR as a general tool and a subset of 32 isolates with a common specific IS 6110 strain type in Ireland. Within the group of 62 isolates, pUCD-DR identified 42 strains and was comparable to both IS 6110 (41 strains) and polymorphic guanine-cytosine-rich sequence (PGRS) (37 strains) analysis. pUCD-DR was found to be comparable to IS 6110 and PGRS in identifying four separate clusters of isolates which were confirmed to be clinically related. pUCD-DR divided the common IS 6110 isolates into six distinct types and was comparable to PGRS (seven strain types). The usefulness of this probe as an epidemiological tool is discussed.