Abstract: Methods for identification or detection of a species of an organism or a group of related species of an organism by species non-specific amplification of a target sequence followed by species- or group-specific detection of the amplification products. Also provided are a target sequence which is amplifiable in multiple species of mycobacteria using a single pair of amplification primers and species- and group-specific detector probes for hybridization to the assay regioin of the amplified target. Blocking oligonucleotides are employed to allow discrimination among species in which the amplified target sequences are sufficiently similar that they cross-hybridize to an assay probe.