We consider a smooth reversible vector field in R^4, such that the origin is a fixed point. The differential at the origin has two double pure imaginary eigenvalues ±iq for the critical value 0 of the parameter µ. We show, by a normal form analysis, that the vector field can be approximated by an integrable field in R^4, for which we know all solutions. Specially interesting ones are the homoclinics to 0, and homoclinics to periodic solutions, depending on the sign of a leading nonlinear coefficient. We prove in particular the persistence of these homoclinics for the full vector field.