Male and female hooded rats were intraperitoneally injected with 0 (vehicle only), 5 or 10mg/kg d-cycloserine (DCS) and then individually allowed free access to the arms of a Y maze (acquisition trial), one of which was black and the other white. Their ability to later recognize the arm that had changed from white to black was assessed from the first arm entered, and the number of times the novel changed arm was repeatedly entered as well as the total time they spent in this arm. DCS increased the number of times the novel arm was entered first and, at the higher dose, repeated entries of and time spent in this arm by female rats. Males showed increases after the lower but not higher dose. In a second experiment, DCS was administered after rather than before the acquisition trial. With the exception of the first arm entered for males only, DCS did not significantly affect choices of the novel arm. However, contrary to treatment with vehicle, such choices were significantly higher than chance expectancies after 5mg/kg DCS, thereby indicating that the treated rats were able to recognize the novel arm. It was concluded that, in the first experiment, DCS had mainly improved attention and/or encoding, and had slightly enhanced memory in the second. Any effects on memory were most likely due to prevention of forgetting. There was also evidence of anxiolytic effects of DCS that may have facilitated responses to both arms without affecting specific choices of the novel alternative.