Based on the saturable photorefractive nonlinearity for photovoltaic crystals under short-circuit condition, the general (on- and off-axis) Z-scan formula for a one-dimensional Gaussian laser beam is derived. The bulk photovoltaic field in an iron doped lithium niobate crystal is estimated from Z-scan experiments. The possibility to use the Z-scan technique to detect and measure the bulk photovoltaic effects in pyroelectric crystals with photorefraction is discussed. (C) 1997 Elsevier Science B.V.14141795292297