The goal of this study is to conduct a prospective, open-label 6-month trial of rituximab in patients who present with symptomatic primary or idiopathic PAP. A total of 10 subjects with primary PAP will be enrolled over 12 months at East Carolina University. Patients over age 18 with a clinical diagnosis of moderate symptomatic idiopathic PAP, established by appropriate clinical history, radiographic and physiologic findings, presence of circulating anti-GM-CSF antibody, and confirmatory findings on bronchoscopy with bronchoalveolar lavage and/or open-lung biopsy will be recruited. Patients with newly diagnosed PAP or established disease may be considered for this study.