In-vivo 31P-NMR spectroscopy of the spleen was carried out in 15 patients with splenomegaly from various causes (Hodgkin's disease, non-Hodgkin lymphoma, polycythaemia vera, chronic lymphatic leukaemia, chronic myeloid leukaemia). Volume selection was with the ISIS technique, voxel size was between 3 x 5 x 5 and 8 x 6 x 7 cm3. There was a markedly elevated (PM+Pi)/beta-NTP quotient (mean 3.41 with a standard deviation of 0.37) (p < 0.001) and raised PDE/beta/NTP quotient as compared with 8 normals, who showed an (PME+Pi)/beta-NTP quotient of 2.32 and a PDE/beta/NTP quotient of 1.11. These raised quotients were interpreted as indicating increased membrane phospholipid metabolism due to increased cell turnover. The data suggest there may be some clinical value in performing 31P-NMR spectroscopy for defining splenic involvement in myeloproliferative diseases but further confirmatory studies will be necessary.