To determine the relationship between MR relaxation times and the iron content of the spleens in patients with thalassemia, we measured these parameters at 0.19 and 1.18 T in 19 thalassemic spleen specimens in vitro. The correlation was best between iron content and the dependence between the interecho interval and the 1/T2 (T2 relaxation rate) at 1.18 T(r = .9361, p less than .001). No statistically significant correlation was found between T1 and iron content at either field strength. The variation of the 1/T2 with interecho interval may be useful for measuring iron content in vivo. It supports the theory that the T2 relaxation of iron deposits occurs via cellular field gradients produced by intralysosomal granules of hemosiderin.