on the occasion of his 60th birthday Streszczenie Let (X, d) be a proper ultrametric space. Given a measure m on X and a function B → C(B) defined on the collection of all nonsingleton balls B of X, we consider the associated hierarchical Laplacian L = L C . The operator L acts in L 2 (X, m), is essentially self-adjoint and has a pure point spectrum. It admits a continuous heat kernel p(t, x, y) with respect to m. We consider the case when X has a transitive group of isometries under which the operator L is invariant and study the asymptotic behaviour of the function t → p(t, x, x) = p(t). It is completely monotone, but does not vary regularly. When X = Q p , the ring of p-adic numbers, and L = D α , the operator of fractional derivative of order α, we show that p(t) = t −1/α A(log p t), where A(τ ) is a continuous non-constant α-periodic function. We also study asymptotic behaviour of min A and max A as the space parameter p tends to ∞. When X = S ∞ , the infinite symmetric group, and L is a hierarchical Laplacian with metric structure analogous to D α , we show that, contrary to the previous case, the completely monotone function p(t) oscillates between two functions ψ(t) and Ψ(t) such that ψ(t)/Ψ(t) → 0 as t → ∞ .