In addition to the previously reported symmetrical beta-carboline dimer 1, an ascidian Didemnum sp. yielded trace amounts of beta-carboline and the nonsymmetrical beta-carboline dimers 2, 3, and 5. The structures of the nonsymmetrical dimers were confirmed by nonselective synthesis of 2 and 3 from beta-carboline, which also yielded additional dimers 4 and 6.