Using high-resolution two-dimensional polyacrylamide gel electrophoresis we studied the polymorphism of protein amounts in some genotypes of maize and pea. This type of variability seems to be rather common and insensitive to environmental conditions, as attested by the comparison of the patterns of two maize lines harvested in two different years. A large-scale experiment involving 5 lines, 7 of their hybrids, and 6 organs (or physiological stages) of maize allowed us to examine numerous polypeptides regrading their genetic variability, their amount differences between organs and the inheritance of their abundance. Genetic and organ variations are not independent: polypeptides whose amount varies from one organ to another are, for the most part, genetically variable (59 %), while the stable polypeptides are not often genetically variable (18 %). We found a striking organ specificity for (i) the extent of quantitative variability (from 2.3–15.4 % of the polypetides), (ii) the occurrence and the type of variation for a given polypeptide (an intensity difference seen in an organ can disappear or even be reversed in another one), (iii) the kind of inheritance (additive/non-additive): combining the 6 organs and the 7 hybrids we found 101 cases of non-additivity (4 % of the total) which conecern as many as 72 different spots, that is to say that in most cases a polypeptide displaying nonadditivity in an organ seems to display additivity in the other ones. Moreover, for most of the polypeptides with nonadditive inheritance the hybrid spot presents an intensity similar to that of the most intense parental spot. Thus for protein experssion a hybrid cannot be predicted from its parents. The organ-specificity was also evidenced by analyzing pleiotropic effect of gene substitutions in various organs of garden pea. Comparisons of isogenic lines differing for the r-locus revealed that according to the organ, the gene substitution caused appearances, disappearances or quantitative changes for 0 % to more than 10 % of the proteins revealed. All these features are discussed in connection with the possible role of variation of protein amounts in phenotypic variability.