Degenerate time-dependent Lagrangians of second order: the fourth order differential equation problem Manuel de Le\'on \and Juan C. Marrero Abstract. We develop a constraint algorithm for degenerate time-dependent Lagrangians of second order and solve the so-called fourth order differential equation problem. The study is inspired in the Gotay and Nester constraint algorithm and the notion of intermediate spaces introduced by Gr\`acia, Pons and Rom\'an-Roy. Keywords. Degenerate, time-dependent, higher order Lagrangians, constraint algorithm. MS classification. 58F05, 53C15, 53C05, 70H35.