Along with the "trivial" temperature hysteresis of the dielectric constant resulting from the first-order phase transition there is a hysteresis of in the polar phase of KDP crystals grown with a large growth rate. This type of hysteresis, which is absent from traditionally (slow rate) grown crystals is enhanced in dye doped crystals where the organic dyes change the domain contribution to the dielectric constant below T C . This temperature hysteresis of is similar to the global hysteresis observed in ferroelectrics with an incommensurate phase.