The effects of different nitrogen sources on growth and sclerotial production by Aspergillus niger were determined on a synthetic agar medium. The organism used inorganic, organic, and ammonium nitrogen for growth and sclerotial production. Among the ammonium compounds tested, the chloride, phosphate, sulfate, and carbonate were used poorly, but the nitrate was well utilized. Addition of organic acids to ammonium compounds increased sclerotial production. Raising the concentration of sodium nitrate to a certain level (0.15%) increased the number of sclerotial initials and the number and weight of those which matured. Sodium nitrite curtailed mycelial growth and prevented production of sclerotia. Utilization of nitrite was accelerated by adjusting the pH on the alkaline side from 7.5 to 9.0. Urea supported poor sclerotial production; thiourea inhibited it. Of the amino acids, histidine yielded the most and arginine the least number of sclerotia. In lysine medium, the white cottony sclerotial initials remained fluffy even after 20 days. Sclerotial production decreased significantly when proline, glutamic acid, or leucine were omitted from the basal medium containing 10 amino acids. In general, no correlation existed between the number of sclerotia formed and the dry weight they attained on different nitrogen sources. With certain nitrogen sources sclerotial initials failed to mature.