Christopher Roberts, 19, of Great Dockray, Penrith, and Karen Irvine of Lark Field, Penrith, also 19, both pleaded not guilty to murdering four month old Lukas Irvine on November 21, 2010.
The baby was admitted to the Royal Lancaster Infirmary on November 17 last year after being found collapsed at an address in the Scotforth area of Lancaster. He died on November 21.
They also pleaded not guilty to a charge of causing or allowing the death of the child. A trial is expected to last two weeks.