This study analyses the secondary price formation process of IPOs on the first trading day for a sample of 67 IPOs placed on the Spanish stock market. Our findings, after stating that the undervaluation does not go beyond the first trading day and that the intraday or secondary (open-toclose) return is significantly positive, show that intraday price variation, observed through open-to-close return variable, is not related to the offer and firm characteristics. Nevertheless, the influence of the primary market over the secondary price formation process on the first trading day is quite evident. In particular, we observe that the combination of cold and primary (offer-to-open) return variables allows us to partly explain the intraday price variation and that our results are fully consistent with the price support arguments for cold IPOs and, to a lesser degree, the casca - de effect for hot IPOs.

Key words: initial public offerings (IPOs), underpricing, cold IPOs, hot IPOs, intraday or secondary return.
JEL Classification: G12, G14, G24.