Medical oncology patients experiencing pain frequently report nocturnal sleep disturbances and daytime sleepiness that adversely affect their functional health status (FHS) and quality of life (QOL). Furthermore, sleep disturbances may lead to increased subjective sensations of pain. Opioid analgesics are known to have intrinsic properties that negatively affect sleep quality. However, they can exert a positive effect on sleep by relieving pain. Therefore, pain and opioids can be viewed as two factors independently affecting nighttime sleep daytime wakefulness while also interacting with each other. The purposes of this descriptive comparative study are to examine pain and opioid use in relation to sleep and wakefulness and to examine associations between daytime and nocturnal sleep and FHS and QOL. The sample will include 80 medical oncology subjects who take opioid analgesics for cancer related pain and report a daily worst pain score or <3 or >6 on a scale of 10. All subjects who meet the entrance criteria will be screened by one night of laboratory-based polysomnography to eliminate those with severe periodic leg movement disorder or sleep apnea syndrome. Those subjects meeting all criteria to continue in the study will undergo a laboratory based multiple sleep latency test the following day to index subjects' physiological sleepiness as well as complete brief pain and sleep surveys and QOL and FHS inventories with documented reliability and validity. Subjects will then be monitored for one 48 hour period in their usual home environments via ambulatory polysomnographic equipment and will make entries in a pain and sleep diary. The study will examine the extent to which pain intensity and opioid use are independently associated with day and night time sleep as well as the relationships between sleep and wakefulness and FHS and QOL. Given the centrality of opioids to cancer pain management, detailed analyses of the associations between pain and opioids and sleep and wakefulness in medical oncology patients are needed to develop optimal treatment regimens that maximize the benefits of pain relief while minimizing side effects of sleep disruption. Finally, the results of the study will assist in furthering the development of theory regarding sleep regulatory processes.