Partial decode-and-forward (PDF) is known to achieve the capacity of two classes of relay channels, namely the semideterministic relay channel and the relay channel with orthogonal components at the source. In this talk, we present a new class of relay channels where PDF is optimal, which we call less noisy relay channels, where the channel seen by the relay is stronger than that seen by the destination in a certain sense, which resembles the condition for the less noisy broadcast channels. We show an example of a relay channel that belongs to this class where decode-and-forward is strictly suboptimal but PDF is capacity achieving.