This note establishes a stronger version of a conjecture of Reid and others in the arithmetic case: if two elements of equal trace (e.g. conjugate elements) generate an arithmetic two-bridge knot or link group, then the elements are parabolic (and hence peripheral). This includes the figure-eight knot and Whitehead link groups. Similarly, if two conjugate elements generate the trefoil knot group, then the elements are peripheral. Theorem 1.1. If M is a compact, orientable, irreducible 3-manifold with incompressible boundary and π 1 M is generated by two peripheral elements, then M is homeomorphic to the exterior of a two-bridge knot or link in S 3 .Arising from work on Simon's Conjecture (see Sec. 6 for statement and [11, Problem 1.12]), Reid and others proposed the following conjecture, which for convenience we will call:Reid's Conjecture. Let K be a knot for which π 1 (S 3 K) is generated by two conjugate elements. Then the elements are peripheral (and hence the knot is twobridge by above). 905 J. Knot Theory Ramifications 2010.19:905-916. Downloaded from www.worldscientific.com by THE UNIVERSITY OF OKLAHOMA on 02/04/15. For personal use only. Conjugate Generators of Knot and Link Groups 907 Our application is the following. Corollary 2.3. Let Γ be a finite-covolume Kleinian group whose traces lie in R, the ring of integers in Q(trΓ). If A, B = Γ = X, Y , then 2 − tr[X, Y ] is a unit multiple of 2 − tr[A, B] in R. Proof. By Lemma 2.1, O 1 = R[1, A, B, AB] and O 2 = R[1, X, Y, XY ] are orders in AΓ. Furthermore, d(O 1 ) = 2 − tr[A, B] and d(O 2 ) = 2 − tr[X, Y ] are ideals in R. The Cayley-Hamilton Theorem yields the identity