A miniature pig kidney cell line has been established from porcine fetuses taken aseptically by hysterectomy and maintained for more than 50 passages in Eagle's minimal essential medium containing 10% heat-inactivated newborn calf serum. Cell transfers were performed each week. Primary and serially passaged cells were found to be highly refractory to infection by Chlamydia trachomatis strains TW-3, Bour, and LGV 440L and Chlamydia psittaci strains meningopneumonitis and 6BC and insusceptible to poliovirus type 1. The cells were susceptible to vesicular stomatitis virus and herpes simplex type 1 virus. Identity of the cells was established by cytotoxicity, isozyme, and cytogenetic studies.