AbstractSynthesis and organ distribution of the oxidation products of methylruthenocene up to ruthenocene acid and of various derivatives of hydroxymethylruthenocene labelled with103Ru are described. Hydroxymethylruthenocene and ruthenocenecarboxaldehyde show like ruthenocene acid a comparable organ distribution and a high affinity to the kidneys. Probable hydroxymethylruthenocene and the aldehyde are oxidizid in vivo and then excreted as acid or as conjugate via kidneys. The benzoic acid ester of hydroxymethylruthenocene enriches in the adrenals with high contrast to kidneys. Tumor affinity of all compounds tested was low.