The effect of a periodic liquid feed on the effective radial heat conductivity, Lambda(r), in a trickle bed was investigated. The mean Lambda(r) under periodic operation was found to be well estimated by time-weighed averaging of steady state values. The actual effect of periodic operation can therefore be predicted by the shape of the Lambda(r), u(L) - curve in steady state operation. The effect of periodic operation is attenuated with decreasing gas flow rates and with decreasing liquid flow rate amplitudes in a bed of spherical particles. Practically no effect was observed with cylindrical particles.