We find exact analytical expressions for mixing angles in matter in the context of three generation neutrino oscillations in matter to discuss the role of resonances in this phenomenon. We show that some knowledge from conventional two neutrino MSW effect, which has been extended to approximated solutions to three neutrino oscillations, has to be abandoned in this exact approach. We observe that maximal values for the mixing angles in matter are found in nonresonant regions and stationary phases do not coincide anymore with resonances in this simple extension of the MSW effect. We present a general way to identify a resonance and discuss what we can physically expect in these regions