Following a period as a research scientist at the Tenovus Institute for Cancer Research in Cardiff, Wales, Euan ultimately becoming its Deputy Director. In 1974 he became Director of the NHS Regional Hormone Laboratory in Edinburgh establishing a specialist analytical service for clinicians in SE Scotland while continuing his research work on the development of immunoassays for the measurement of minute concentrations of therapeutic drugs in human blood. As a Senior Lecturer in Endocrinology in the University of Edinburgh he combined his NHS duties with that of undergraduate and postgraduate teaching, and was latterly involved in the development of UK Interlaboratory Quality Assessment Schemes.

In 1978 he joined Amersham International plc. as QC Manager for the company's new facility at Cardiff where approximately 50% of its products were manufactured, including its complete range of chemicals and biochemicals labelled with ¹⁴C or ³H, and all of their in vitro diagnostic products (IVD's). In 1983 he became Production Manager and then QA Manager for the newly formed IVD Division, and in 1988 was responsible for the Division's successful campaign to gain registration of compliance with ISO9001, Amersham being the first IVD company in the world to achieve this. He currently sits on BSi committee CH/210/1 as a representative of the UK Department of Health.