Let K be a field, m and n positive integers, and X = {x 1 , . . . , x n }, and Y = {y 1 , . . . , y m } sets of independent variables over K. Let A be the localized polynomial ring K[X] (X) . We prove that every prime ideal P in A = KJXK that is maximal with respect to P ∩ A = (0) has height n − 1. We consider the mixed power series/polynomial rings B := KJXK[Y ] (X,Y ) and C := K[Y ] (Y ) JXK. For each prime ideal P of B = C that is maximal with respect to either P ∩ B = (0) or P ∩ C = (0), we prove that P has height n + m − 2. We also prove each prime ideal P of KJX, Y K that is maximal with respect to P ∩ KJXK = (0) is of height either m or n + m − 2.