Cultivar differences in fruit malformation in tomato were studied using 5 cultivars with multilocular and oligolocular fruits. When the seedlings were exposed to low temperature, occurrence of fruit malformation was severe in multilocular cultivars (`Ponderosa' and `Ogatafukuju') but it was slight in oligolocular cultivars (`Kyokko' and `Sweety'). When the seedlings were treated with TIBA (2, 3, 5-triiodobenzoic acid) and GA3 (gibberellic acid), `Ponderosa' and `Ogatafukuju' also showed severer fruit malformation than the other oligolocular cultivars. `Ogatafukuju' , which showed a higher degree of fruit malformation than `Kyokko', accumulated more total sugar and gibberellin in the shoot apex when the seedlings were exposed to low temperature.