The study investigated neuropsychological performance in chronic nonmalignant pain patients receiving long-term oral opioid therapy. Forty patients treated solely with regular and stable doses of an oral opioid were compared with 40 healthy volunteers. The patients received daily opioid doses of 15-300 mg of oral morphine (median: 60 mg) or equianalgesic doses of other opioids. The neuropsychological tests consisted of continuous reaction time (CRT), which measured vigilance/attention; finger tapping test (FTT), which measured psychomotor speed; and paced auditory serial addition task (PASAT), which measured working memory. Three months after the study had been carried out, 14 of the controls were retested in order to determine the reliability of the three tests. The patients performed statistically significantly poorer than the controls in all the tests. Significantly positive correlations were found between the PASAT and pain visual analogue scales (VAS). In the retesting of 14 controls, it was found that the tests showed high reliability. Vigilance/attention, psychomotor speed, and working memory were significantly impaired in chronic nonmalignant pain patients. The present study cannot determine which factors influenced the test results, but pain itself seemed to have an arousal effect on working memory.