This paper describes the development of a wireline tool for open-hole stress measurements. This tool includes a straddle packer module comprising surface controlled valves, pressure gauges, and a downhole pump. Stress measurements are either based on the micro-hydraulic fracturing technique or the H.T.P.F technique (Hydraulic Tests on Pre-existing Fracture). Before presenting the tool, we derive specifications for obtaining reliable stress measurements. The maximum differential pressure (which is the interval pressure minus wellbore pressure) that the tool can currently sustain is 28 MPa (4000 psi) and flow rates of the order of 1 liter/min can be achieved. Results of field tests are described which demonstrate the high quality of the tool response.