Our aim in this paper is to improve on the algorithms for the computation o
f SAGBI and SAGBI-Grobner for subalgebras of polynomial rings in the specia
l case where the base ring is a principal ideal domain. In addition we will
show the existence in general of strong SAGBI bases (the natural analogue
of strong Grobner bases) over a PID. (C) 1999 Academic Press.