Spatially and temporally resolved measurements of runaway electrons have been performed in the TEXTOR tokamak. The main diagnostic for the investigations is a newly developed runaway probe which is mounted at a reciprocating mechanism. In addition, the runaway electrons are studied in the plasma by synchrotron emission. The scanning probes consists of fluorescing crystals covered by a graphite housing and is located at different radial positions. In this study, two generations of the probes are presented, a simple one for proving the principle and a more advanced one which allows the measurement of the energy distribution of the runaways. A strong decay of the runaway electrons at the plasma edge was observed. Runaway electrons have been measured at different plasma densities by synchrotron radiation and the probe. The reduction of the number of runaways have been measured with increasing plasma densities during low density plasma discharges by both diagnostics. The spectrum of runaway electrons produced during low density plasma discharges was measured. Finally, measurements of runaways with high temporal resolution of 0.05 ms have been carried out during a disruption discharge.