My daughter has been bit SEVERAL times by the same boy at her day care. It was horrible because her providers had tried SO hard to keep him away from her. He was 2 when it started and she was little (6 months), she was in the exersaucer and he was playing near her and he just scooted over to her and bit her foot. He continued to stealthily gain proximity to her to bite her on other occasions, once while she was one of the women's lap, another when she was in the high chair! He got time outs, but it didn't address the problem. I hated to confront his parents about it (because I knew the provider had), but I did. They were upset, but didn't know what to do. He still has this issue, but my daughter can walk and talk now and has clobbered him once when he got near her to bite--so now he's moved on to another littler one. Seems disturbing to me, like he targets the ones who can't defend themselves because it's easier and he gets some sort of satisfaction out of it. Does it seem like your son is targeting his playmate? What is the context of the biting?
Monitor him closely. Figure out the situations that seem to trigger it. If it's frustration or anger--you might actually have an easier time than the parents of the boy at daycare! Also, ask your peditrician about it and what he/she recommends you can do.
On a funny note, my brother (14 months younger) bit me a couple times when we were toddlers and once left teeth marks in my arm. My mom, a FEISTY Spaniard who grew up in Mexico, grabbed him, dragged him to the kitchen and put a jalapeno pepper in his mouth and told him to bite it. He never bit me--or anyone again! He's not scarred for life, and started eating salsa with jalapenos when he was about 10 (well past the biting phase!).
Good luck to you and your little boy.