While the human genome is mostly the same in all people, slight differences exist. This genetic variation makes up about onetenth of a percent of each person's DNA. Monozygotic (MZ) twins have been used to demonstrate the role of environmental factors in determining complex diseases and phenotypes, but the true nature of the phenotypic discordance nevertheless remains extremely poorly understood. In the current study total proteins of four identical twins were analyzed using SDS-PAGE. The results indicated a similar pattern in each pair of studied twins however; differences in the intensities of protein expression were detected among two pairs of analyzed twins. The study concluded that some factors might lead to differences between MZ twin's phenotypes leading to detectable modifications and thus modulating the genetic information.