A novel rapidly growing, non-pigmented mycobacterium was isolated from blood samples obtained from 17 patients with febrile syndrome. Bacterial growth occurred at 30 and 37 degrees C on Löwenstein-Jensen medium and also on MacConkey agar without crystal violet. Strains contained alpha- and alpha'-mycolates in their cell wall. Sequence analysis of the hsp65 and 16S rRNA genes identified the isolates as rapidly growing mycobacteria. Sequences of both genes were unique within the mycobacteria. DNA-DNA hybridization showed that the isolates had less than 15 % reassociation with 13 other recognized rapidly growing mycobacteria. The name Mycobacterium canariasense sp. nov. is proposed for this novel opportunistic pathogen, which is most closely related to Mycobacterium diernhoferi. The type strain is 502329T (= CIP 107998T = CCUG 47953T).