The q-analogues of modified Bessel functions and Macdonald functions a
re defined in this paper. As in the case of q-Bessel functions introdu
ced by Jackson, there are two kinds of these functions. Like their cla
ssical prototypes, they arise in harmonic analysis on quantum symmetri
c spaces. The definition is based on the power series expansion. Recur
rence relations, difference equations, and q-Wronskians are obtained,
as well as analogues of asymptotic expansions, which are convergent se
ries if q not equal 1. Some relations for basic hypergeometric series,
which result from this, are given.