Abstract. We show that the generalized Fermat equations with signatures (5, 5, 7), (5,5,19), and (7, 7, 5) (and unit coefficients) have no non-trivial primitive integer solutions. Assuming GRH, we also prove the nonexistence of non-trivial primitive integer solutions for the signatures (5, 5, 11), (5,5,13), and (7, 7, 11). The main ingredients for obtaining our results are descent techniques, the method of Chabauty-Coleman, and the modular approach to Diophantine equations.