Abstract.We study the distribution of elements in an additive arithmetical semigroup (G, 6) (as introduced by John Knopfmacher) in whose canonical decomposition the degrees of the prime elements belong to a given union of residue classes mod k. Uniformity cannot be expected, a fact which is exhibited by the example K(1; 4) < K(3; 4).In the present article, we are going to solve the analogous problem in arithmetical semigroups (G, 8) with axiom A # ([3], p. 7). For the reader's convenience we repeat what it means: G is a commutative semigroup with identity e. It contains a subset P (the set of prime elements p of G) which is such that every element -r e of G can be written uniquely apart from the order of factors as a product of elements of P. ~ is a mapping G ~ ~0 such that (1) ~3(ab) = 8(a) + 8(b) for all a,b~G.(2) 7(n):= #{9~GIc~(9) = n} < oo for all n~No.This implies 8(a)=0 iff a =e. In particular, 7(0)= 1 and G is countable.1991 Mathematics Subject Classification: 11N45 (11N25).