Two actinomycete strains isolated from two patients with lung nocardiosis between 1995 and 1997 in Japan were assigned to novel species of the genus Nocardia based on morphological and chemical criteria. Comparative 16S rRNA gene sequence analysis of the two strains revealed that they belong to the genus Nocardia and are most closely related to the species Nocardia beijingensis. Determination of DNA-DNA relatedness indicated that these strains could be assigned to two novel species. Based on their phenotypic and phylogenetic characters, two novel species of the genus Nocardia are proposed: Nocardia araoensis sp. nov. for IFM 0575(T) (=NBRC 100135(T)=JCM 12118(T)=DSM 44729(T)) and Nocardia pneumoniae sp. nov. for IFM 0784(T) (=NBRC 100136(T)=JCM 12119(T)=DSM 44730(T)).