  The c-axis optical conductivity and d.c. resistivity are calculated within
the t-J model assuming that the interlayer hopping is incoherent. Use is made
of numerical results for spectral functions recently obtained with the
finite-temperature Lanczos method for finite two-dimensional systems. In the
optimally doped regime we find an anomalous relaxation rate, suggesting a
common relaxation mechanism for intra- and interlayer transport. At low doping
a pseudo-gap opening in the density of states appears to be responsible for a
semimetallic-like behavior of d.c. resistivity.
