We describe the influence of pore shape in the hen's eggshell on calculated resistance to diffusion. These calculations are based on measurements of 70 pore casts, pictures of which were published by Tyler (In: Recent Advances in Food Sciences, Butterworth, London, Vol. 1, 1962). Single-pore resistance was estimated from Fick's first law as the summed resistances of 100 cylindrical segments in series and the calculated boundary layer resistance at the pore apertures. In addition, we constructed an average pore profile from all measurements. The calculated average single pore water vapor conductance (3.2 micrograms X day-1 X torr-1) is about twice the measured literature value. The presence of organic material in the pore openings is discussed as one of several possible reasons for this discrepancy. Average diameter should not be used to calculate conductance of trumpet-shaped pores. The narrow part of the pores plays a dominant role in total pore conductance, and pore shape must be taken into account when estimating conductance from pore dimensions.