RUBÉ N CHÁ VEZ-ZAMARRIPA, J. ANGÉ LICA RAMOS-SALAS, JOSÉ TALAMANTES-SILVA, SALVADOR VALTIERRA, and RAFAEL COLÁ S Dendrite coherency point in an aluminum-silicon-copper casting alloy was determined by analyses of the variation of the thermal diffusivity. The analysis was carried out using the readings of three thermocouples inserted at equal distances in a mould holding the alloy left to solidify. The values obtained by this method are confirmed by metallographic observations on samples left to solidify to the coherency point before plunging them in water.