Embryonic human spinal cord cells have been grown in dissociated monolayer cultures for 1 to 7 weeks. Using cell type specific markers, it was possible to show that the cultures contain neurons, astrocytes and fibroblasts. Electrical membrane properties were studied with patch electrodes using the whole cell recording technique. Neurons had short duration action potentials that could be blocked by tetrodotoxin. The membrane currents in these neurons were studied in voltage clamp experiments. Three types of voltage-dependent currents were observed: a sodium current; a potassium current made up of two components, IA and IK; and a calcium current. Both cholinergic and GABAergic neurons are present in the cultures. There is more choline acetyltransferase activity in cultures prepared from the anterior as compared to the posterior part of the spinal cord, suggesting that the cultures contain motoneurons. This tissue culture preparation was developed for the study of amyotrophic lateral sclerosis; we have been unable to detect the presence of any toxic agent from the serum of these patients on the cultured cells. Experiments are in progress to purify the motoneurons using Percoll gradients.