The behavior of fatigue crack growth for low and medium carbon steels, an austenitic stainless steel and an aluminum alloy under pure Mode I1 loading was investigated experimentally, using cruciform specimens. The results show that under pure Mode I1 loading, fatigue crack propagation has three possibilities, namely, bifurcation into two branches, propagation along the original Mode I1 direction, and the mixture of these two situations, depending on the material. The growth rate da/dN vs. AK, relation for Mode I1 propagation is similar to a Pans type law for Mode I growth. Fractographic observations by optical microscopy and SEM were made also on all specimens tested. When a crack branched, striations parallel to the crack front which were often associated with Mode I fatigue crack growth were observed and long marks parallel to the crack propagation direction were also found for slanted fracture surfaces. When a crack propagated along the original Mode I1 direction, many frictional marks parallel to the crack propagation direction were observed.