To explain how symptoms, lung function, mood, and social support affect level of functioning, patients (N = 143) with chronic obstructive pulmonary disease (COPD) completed measures assessing their symptoms (Bronchitis-Emphysema Symptom Checklist), mood (Profile of Mood States), social support (Personal Resource Questionnaire), and functioning (Sickness Impact Profile). Those who were receiving oxygen therapy (n = 52) had significantly lower FEV1 scores and experienced significantly poorer functioning than those who were not receiving oxygen therapy (n = 91). Results of path analyses indicated that symptoms and mood directly, and social support indirectly, influenced the functioning of those who were not receiving oxygen. For those who were receiving oxygen, only symptoms directly, and FEV1 indirectly, influenced their functioning. These models need to be confirmed using other samples of patients with COPD.