This study examined the electrical properties and Na+ transport function of a porcine trophectoderm cell line, TE1, which forms a polarized epithelium in culture. Specifically, the capacity of TE1 cells to generate a transepithelial potential difference, and to modify selectively the Na+, K+ and Cl- ionic composition of medium in the apical and basolateral compartments, was examined over a 48-h period using monolayers cultured on permeable tissue culture supports. TE1-cell monolayers formed 'tight epithelia' in that significant transepithelial electrical resistances (RT; median value 5.30 k(ohms)/cm2, range 2.26-9.18 k(ohms)/cm2, n = 72), and electrical potential differences (VT; maximum mean value at 24 h, 42.9 mV, SEM 7.14; n = 6) were generated. It is concluded that: (1) the VT was generated by the amiloride-sensitive, Na+ absorptive function; (2) K+ transport across the monolayers was related to the electrogenic Na+ transport function; and (3) the three ions traverse the epithelium by active transport or co-transport, rather than simple diffusion. These data substantiate the proposed role for porcine trophectoderm of generating electrical and chemical potentials in vivo, and for regulating the environment of the blastocoel cavity in the pre-implantation porcine embryo.