Isothermal transformations of supercooled 1-butanol were observed by positron lifetime spectroscopy. Transformation rate is the highest near 150 K, whereas below 140 K it slows down becoming undetectable below 120 K. At the temperature range of 123-135 K the ortho-positronium lifetime achieves the final value which is higher than the one observed for crystalline phase. This is an indication of transition to a new ( meta) stable structure, in which the ortho-positronium lifetime and intensity reach values that are intermediate between liquid and crystal phases. Consistency of positron annihilation data with the concept of two coexisting phases is discussed. (C) 2010 Elsevier B. V. All rights reserved.