AbstractMarrow iron was assessed in needle biopsy sections and in simultaneously obtained aspirated smears and aspirated clot sections from 251 patients. Significantly different amounts of stainable iron were observed in needle biopsy sections and aspirated smears in 15% of the specimens. The usual difference consisted of significantly less stainable iron in needle biopsy sections as compared to the aspirated smears (13%). Of clinical importance was the finding of absent stainable iron in 8% of the needle biopsy sections, in contrast to the definite deposits observed in the corresponding aspirated smear. Of similar interest was the observation that 6% of the needle biospy sections had significantly less stainable iron than corresponding hemosiderotic smears. The amounts of stainable iron in needle biopsy sections were similar to the amounts observed in the corresponding aspirated clot sections. Evaluation of marrow iron using needle biopsy sections as well as aspirated clot sections differs from results observed in aspirated smears and could be a source of significant error in the assessment of iron stores.