Preservation by low temperature vitrification is being developed for the cryopreservation of mammalian organs. The purpose is to avoid ice crystallization, which can cause damage during cooling or warming. With the high cryoprotectant concentrations being used, crystallization is easily avoided during cooling, but not during rewarming at practical warming rates. Assessment of the amount of crystallization occurring during warming is therefore necessary. 1,3-butanediol is a good glass-former and a good cryoprotectant for red blood cells. Similar to 1,2-propanediol, it has already been used for the vitrification of erythrocytes. As a model, the crystallization kinetics of warming vitreous solutions are presented here for concentrations higher than 38% ( w w ) 1,3-butanediol. Isothermal and continuous heating rate (CHR) experiments have been performed by differential scanning calorimetry and by direct optical observation using a cryomicroscope. For the isothermal method, the Johnson-Avrami equation and its second derivative were used for thermal analysis. For the CHR approach, the isoconversional method was used, assuming always a Johnson-Avrami variation for the crystallization fraction. The calorimetry results were then compared with the cryomicroscopy observations, allowing a determination of the exponent n. The isothermal approach gives higher calculated parameters than the CHR approach. By the isothermal approach, the Avrami exponent n varies between 2.5 and 3 and the “ctivation energy” E ★ decreases from 16.9 to 11.5 kcal mol −1. By the CHR approach, n increases from 1.8 to 2.5 and the various methods used give similar results for E ★, with the same variations in polyalcohol concentrations as with the isothermal method. With the isothermal method, a break point is observed for both E☆ and n, determined from calorimetry, at 44–46% 1,3-butanediol. This corresponds to a change in the kinetics of the crystallization observed by cryomicroscopy.