Cryptic genetic variation may be an important component of adaptive, deleterious, or neutral variation that is contingent upon environmental or genetic circumstances to be expressed. We are conducting screens for inducible, phenotypic variation in natural populations of Drosophila melanogaster. The screen is based on a model for the production of head defects by the extra eye mutation (ee), which is incompletely penetrant, variably expressed, and conditionally dominant. The proposed epigenetic model predicts that new mutant phenotypes may be uncovered in crosses between ee lines and flies from natural populations that harbor P-elements at various genomic locations. Such novel mutants are predicted to be incompletely penetrant and variably expressed, caused by epigenetic silencing of genes residing at genomic positions near P transposable elements. In an initial study described here, we conducted a screen for such mutations by scoring flies in lines established from crosses of 40 separate, wild-derived lines from various geographic coordinates to ee. In several such lines, new mutations were recovered that exhibit epigenetic properties. The induction of these mutant phenotypes by crosses to ee was repeatable and not observed in control lines, suggesting that they are not induced de novo, but rather represent cryptic phenotypes induced by genetic elements in the ee line. Cby (crybaby) and Bby (Beady), both affecting ventral eye development, were observed in lines derived from Brazil and Australia, respectively. Tby (tumorous baby), obtained independently in a second line derived from Brazil, yields melanotic tumours in ~3-5% of 3rd instar larvae. Our results to date suggest that variation in natural populations may include cryptic, epigenetic sources, which are revealed under particular genetic contingencies. Screens of multiple, wild strains for additional examples of cryptic phenotypes are ongoing, as are genetic and molecular characterizations of mutant phenotypes so far recovered.