We report measurements of out-of-plane (rho(c)) and in-plane (rho(ab)) norm
al-state resistivities of single crystals of insulating PrBa2Cu3O7-delta an
d strongly underdoped oxygen deficient YBa2Cu3O6.41 using a flux transforme
r method. In the superconducting specimens, the onset of superconductivity
was suppressed by a magnetic field of 9 T. We have found that the anisotrop
y rho(c)/rho(ab) of these samples increases monotonically at low temperatur
es with no signs of saturation. The temperature dependence of rho(c)/rho(ab
) for YBa2Cu3O6.41 is well described by rho(c)/rho(ab) = a + bT(-2/3), but
over a smaller temperature range than for insulating PrBa2Cu3O7-delta. Both
the absence of saturation of rho(c)/rho(ab) and its T-2/3 dependence indic
ate two-dimensional conduction. This means that the average in-plane hoppin
g distance of the localized charge carriers increases with decreasing T acc
ording to Mott's (R) over bar similar to T-1/3 law, while the elementary st
ep in the c-direction remains T independent, equal to the spacing between t
he bilayers.