The formation of long-lived (τ ≫ 10 μsec) product ions through associative ionization reactions of the type: K(nd) + BC → (KBC)\sp+ + e\sp− has been investigated for 8 ≤ n ≤ 18, using a variety of polyatomic target molecules (denoted BC). Although such reactions clearly involve the Rydberg core ion, the presence of the Rydberg electron is also essential to stabilize the collision product. Rate constants for these reactions have been measured with the mixed-gas technique and are compared with those predicted by ion-molecule reaction theories. Studies with a number of different target molecules have been undertaken, so as to investigate the factors that influence the rate constants for associative ionization. In particular, it is observed that the rate constants increase with both the dipole moment and complexity of the target, and they also depend strongly on the principal quantum number, n, of the Rydberg state involved.