A new 99mTc labelling method using a cleavable chelator, RP-1, was developed. In this study Balb/c mice with ovarian carcinoma xenografts received various Fab' fragments labelled with 99mTc either directly or via RP-1. Kidney uptake was significantly lower for the RP-1 linked conjugates. Tumour uptake showed no significant differences between RP-1 conjugates and directly labelled preparations. In conclusion, with the use of the cleavable linker RP-1, kidney uptake can be reduced significantly resulting in a lower radiation dose to the kidneys.