[en] Aim. - The U.M.R. 484 I.N.S.E.R.M. develops a 'cartilage imaging strategy' with the ^99mTc-N.T.P. 15-5 tracer that selectively binds to cartilage proteoglycans, allowing a highly specific cartilage imaging. Since chondro-genic tumours are characterized by the presence of cartilaginous matrix, we hypothesized that the ^99mTc-N.T.P. 15-5 tracer would allow chondrosarcoma imaging, which is currently lacking in clinics. In the rat model of grade II para-tibial chondrosarcoma, we evaluated the relevance of ^99mTc-N.T.P. 15-5 imaging for an early and specific diagnosis of chondrosarcoma. Methods. - ^99mTc-N.T.P. 15-5 longitudinal imaging of animals was performed during two months after para-tibial ortho-topic tumour implantation in the right paw, the left being used as control. At regular intervals, animals were submitted to ^99mTc-M.D.P. bone imaging, the only examination used for SPECT diagnosis of chondrosarcoma in patients. Tumour volume was monitored for two months when the tumours became palpable, with the two perpendicular diameters measured. For both cartilage and bone imaging, the scans were considered positive when areas of tracer uptake were present at sites consistent with the sites of inoculation. For each animal, positive scans were analyzed at each stage using the semiquantitative method of the target to background ratio (T.B.R.), with the target R.O.I. being delineated over the tumour and background R.O.I. over vertebra and muscle. T.B.R. time-course was followed as a function of tumour growth.At study ending, each animal was sacrificed for histopathological control. Results. - ^99mTc-N.T.P. 15-5 scans were positive in 100% of the animals at very early stage (three days) after implantation, while no palpable nor measurable tumour could be assessed. Quantitative analysis of ^99mTc-N.T.P. 15-5 scans evidenced a significant uptake of the tracer at the implantation site at early stage. The time-course of T.B.R. ratios was closely related to tumour growth. It should be high lightened that ^99mTc-M.D.P. bone scans were negative during the whole study. Conclusion. - These experimental results underlined the potential of ^99mTc-N.T.P. 15-5 imaging for both the early and specific diagnosis of grade II chondrosarcoma at molecular level. These results appeared of high interest when one considers the clinical context of chondrosarcoma imaging, where a specific SPECT diagnosis is of real need. (authors)