This study investigates the role of PPARγ in bone metabolism, focusing on its effect on osteogenesis in bone marrow. PPARγ is a key regulator of adipocyte differentiation, and it was found that PPARγ deficiency leads to increased osteoblastogenesis from bone marrow progenitors. Homozygous PPARγ-deficient ES cells spontaneously differentiate into osteoblasts, while heterozygous PPARγ-deficient mice exhibit increased bone mass with enhanced osteoblastogenesis. This effect is not mediated by insulin or leptin and is more pronounced with aging. PPARγ haploinsufficiency enhances osteoblastogenesis in bone marrow cell cultures but does not affect differentiated osteoblasts or osteoclast-lineage cells. The study demonstrates that PPARγ insufficiency increases bone mass by stimulating osteoblastogenesis from bone marrow progenitors. The findings suggest that PPARγ may be a novel target for therapeutic intervention in osteopenic disorders.This study investigates the role of PPARγ in bone metabolism, focusing on its effect on osteogenesis in bone marrow. PPARγ is a key regulator of adipocyte differentiation, and it was found that PPARγ deficiency leads to increased osteoblastogenesis from bone marrow progenitors. Homozygous PPARγ-deficient ES cells spontaneously differentiate into osteoblasts, while heterozygous PPARγ-deficient mice exhibit increased bone mass with enhanced osteoblastogenesis. This effect is not mediated by insulin or leptin and is more pronounced with aging. PPARγ haploinsufficiency enhances osteoblastogenesis in bone marrow cell cultures but does not affect differentiated osteoblasts or osteoclast-lineage cells. The study demonstrates that PPARγ insufficiency increases bone mass by stimulating osteoblastogenesis from bone marrow progenitors. The findings suggest that PPARγ may be a novel target for therapeutic intervention in osteopenic disorders.