The possibility of recoil-labelling with high energy fission fragments has been investigated. We have found that in a mixture of ferrocene with an uranium compound the fission of uranium produces ruthenocene and iodine ferrocene. By this method carrier-free 103Ru(C5H5)2 has been produced. The relative yield of ruthenocen-(103Ru) has been measured with different ratios of uranium to ferrocene, ranging from 0.013 to 0.325. At a ratio of 0.013 about 60% of the total 103-ruthenium are bound in form of ruthenocene. The yield decreases to 45% at a ratio of 0.325. In order to explain these high yields we have to suggest that the labelling is performed not only by the primary fission ruthenium-103, but especially by secondary ruthenium-103 formed by β-decay.