Biological sample collection is becoming more common in epidemiology research to obtain DNA for genetic analysis. There are many different DNA collection methods but little evidence on their relative effectiveness. Therefore, we took the opportunity of a prospective case-control study in myeloproliferative neoplasms (MPNs) to compare DNA yield from 8.5 mL PAXgene tubes for whole blood collection versus 2 mL Oragene OG-500 saliva collection kits. MPNs include polycythaemia vera, essential thrombocythaemia, and primary myelofibrosis. These are rare diseases and our exploratory case-control study (MOSAICC) sought to improve knowledge regarding their aetiology and to determine optimal methodology for a larger UK-wide study. Overall, 233 participants were recruited to the MOSIACC study, and we collected 187 blood and 214 saliva samples. The mean DNA yield from blood was 659.18 ng/μL, significantly higher than the mean DNA yield from saliva samples (275.79 ng/μL). The higher provision of saliva samples might reflect its non-invasive and more convenient nature, compared to blood sample provision. The differences in mean DNA yields might reflect differences in clinical assistance, adherence to instructions, and health status of individuals. In conclusion, both sample collection techniques are simple, effective, and suitable for DNA collection for genetic analysis in future epidemiological research studies but OG-500 kits offer a less invasive alternative for those who refuse to provide blood.