The Seebeck coefficient S of Ca1-xSrxRuO3 (0 less than or equal to x l
ess than or equal to 1) was measured in the temperature range 78 K to
300 K. This coefficient always showed a large bend at about 160 K, irr
espective of the magnetic properties of the sample studied. The differ
ential temperature coefficient dS/dT was found to decrease above this
temperature (S > 0). The usual single-band theory cannot explain this
large bend, and we propose a percolation model in which metallic paths
are composed of parallel-spin arrays, and semiconducting paths are co
mposed of antiparallel-spin arrays.