Are pull ups alone good enough for developing your biceps? There's a lot of evidence out there to suggest that the answer is yes. Pull ups alone -- yes alone -- can be good enough for your biceps. This doesn't mean you shouldn't do curls. By all means, do them. But from my experience, getting an optimal biceps workout can be accomplished with pull ups alone.
My biceps have exploded ever since I began doing pull ups and chin ups consistently. Pull ups, chin ups. close grip chin ups -- and you're done. But don't get carried away. Pull ups put a lot of stress on your central nervous system. Doing them more than twice a week is probably a bad idea!