John Mark Anthony Lenihan FRSE FIP PRPSG OBE (1918–1993) was a British clinical physicist, and science author.
He studied at King's College of Durham University, graduating BSc in 1938.
In 1953 he was promoted to Regional Physicist for Western Scotland and held this role until retiring in 1983.
He employed John Stewart Orr as his senior Physicist, working on radioactive isotopes and doing early research on MRI technology.
His proposers were Anthony Elliot Ritchie, John Currie Gunn, George A P Wyllie and Arthur F. Brown.