Abstract: A well testing apparatus includes a housing having a formation fluid flow passage. A sliding sleeve tester valve is reciprocably disposed in the housing. A probe separable from the housing and constructed to be received coaxially within the sliding sleeve tester valve has a probe passage defined therethrough for communicating the formation fluid flow passage with a measuring device carried on the probe. A probe valve is also disposed in the housing and is constructed to receive a lower end of the probe. A releasable connector operably connects the probe and the sliding sleeve tester valve so that the sliding sleeve tester valve is moved between its open and closed positions in response to reciprocal movement of the probe relative to the housing. The tester valve can be operated an indefinite number of times, and whenever desired the probe can be disconnected from the tester valve in response to an appropriately timed reciprocable motion of the probe.