Erythromycin, food dye, and bacteria were found to enter eggs through certain areas or pores naturally occurring in the shell of most eggs. These absorbing areas were easily blocked by the passage of solutions and by sanding the shell. Removal of cuticle with dilute acid greatly increased shell permeability. A relationship was established between dye spots on the shell membrane and drug level of the egg contents. With white shell eggs, an r value of 0.921 and a regression formula of Y = 2.58 + .668X were determined. The r value for brown shell eggs was 0.808 and the regression formula was Y = 17.08 + 1.68X. Shell thickness had no apparent influence of ERY penetration.