Yttrium-90 is used for palliative therapy for the treatment of skeletal metastases, but because it is a pure beta- emitter, data on the pharmacokinetics and radiation doses to metastases and unaffected organs are lacking. To obtain such data, the present study employed yttrium-86 as a substitute for 90Y, with detection by positron emission tomography (PET). The study compared the properties of two different 86Y complexes - 86Y-citrate and 86Y-ethylene diamine tetramethylene phosphonate (EDTMP) - in ten patients with prostatic cancer who had developed multiple bone metastases (the ten patients being divided into two groups of five). Early dynamics were measured up to 1 h post injection (p.i.) over the liver region, followed by subsequent whole-body PET scans up to 3 days p.i. Absolute uptake data were determined for normal bone, bone metastases, liver and kidney. Radiation doses were calculated according to the MIRD recommendations. Based on the pharmacokinetic measurements of the distribution of the 86Y complexes, it was possible to calculate radiation doses for the bone metastases and the red bone marrow delivered by complexes containing 90Y. In 1 cm3 of bone metastasis, doses of 26+/-11 mGy/MBq and 18+/-2 mGy/MBq were determined per MBq of injected 90Y-citrate and 90Y-EDTMP, respectively. The doses to the bone marrow were 2.5+/-0.4 mGy/MBq for 90Y-citrate and 1.8+/-0.6 mGy/MBq for 90Y-EDTMP. 86Y and PET provide quantitative information applicable to the clinical use of 90Y. This method may also be useful for the design of other 90Y radiopharmaceuticals and for planning radiotherapy dosages.