In one-dimensional superconductors phase coherence is broken by phase-slip events. In the usual strips studied before, the resulting resistance was too small to be measured except in an extremely narrow temperature range near the critical temperature. We study strips with small cross-section and very small mean free path where quantitative comparison with theory is possible over a wide temperature range. Current is passed through the strips and the probability distribution for switching into the dissipative state determined. Results partly agree with predictions for localized occurrence of thermally activated phase-slip. Measurements are extended to lower temperatures to investigate the possibility of phase-slip by quantum tunneling.