Calculations have been performed to determine the transient response of an eddy current probe due to an open subsurface crack in conducting half‐space. In previous work, the transient probe response due to an idea crack was calculated using boundary elements. The ideal crack has zero opening yet acts as a perfect barrier to eddy currents. The theoretical formulation of the problem has now been modified to take account of the fact that the crack may have a significant finite opening. The effects of the opening on the probe response have been investigated. Comparisons with experiment show reasonable agreement. © 2004 American Institute of Physics