Populations of stem cells and methods for their isolation and use are provided. These 
stem cell populations comprise 
aldehyde dehydrogenase positive (ALDHbr) cells isolated from 
bone marrow, and ALDHbr CD105+ cells derived from any 
stem cell source. These populations may also comprise cells expressing such surface markers as CD34, CD38, CD41, CD45, CD105, CD133, CD135, CD117, and HLA-DR, and / or are substantially free from such 
cell surface markers as CD3, CD7, CD 10, CD 13, CD 14, C1319, CD33, CD35, CD56, CD 127, CD 138, and 
glycophorin A. The 
population may also comprise cells expressing CD90. The 
stem cell populations of the invention are isolated from a stem 
cell source such as 
bone marrow, 
peripheral blood, 
umbilical cord blood, and fetal liver. Methods of the invention comprise isolating and purifying stem 
cell populations from stem cell sources, and methods of using these cells to reconstitute, repair, and regenerate tissues.