Participants: Over 650 participants are included in the study, including ME/CFS participants diagnosed by a physician and compliant with CDC '94 (Fukuda) and Canadian Consensus Criteria (CCC), with case definition compliance available for four other commonly-used criteria. Healthy and MS matched controls are also available.

• Mild and Moderate ME/CFS
• Severe (Home-Bound) ME/CFS
• Multiple Sclerosis
• Healthy Controls Samples Available: Over 32,000 aliquots available.
• Whole Blood
• Serum
• Plasma
• RBCs
• PBMCs (Sodium Heparin and K2 EDTA)
• Blood for RNA Extraction (PaxGENE) Associated Data Available:
• Baseline Standard Laboratory Tests to exclude comorbidity causes of fatigue
• In-person clinical assessment data
• Detailed Symptoms Assessments
• Demographic information
• Standardised instruments of Fatigue Severity and Functional Impairment