The stability of Tacaribe virus at different temperatures and the stabilizing effect of calf serum or human albumin were studied. The viral stock employed in this study was a 10% suckling mouse brain suspension prepared in phosphate buffer saline and fractionated in three aliquots: the first was supplemented with 0.5% human albumin, the second with 5% calf serum and the third was maintained without stabilizing agent. The infectivity of Tacaribe virus kept at -70 degrees C was preserved during several months and the reduction in infectivity was not significant even if the viral sample was frozen and thawed four times. However, the addition of an stabilizing protein to the viral stock was necessary to maintain it at -16 or 4 degrees C. Under these conditions, the viral infectivity was completely lost after 3 days when the stock was prepared in phosphate buffer saline alone, while more than 40 days were necessary to destroy the infectivity in presence of serum or albumin. The viral inactivation was completed after 48 hours at 25 or 37 degrees C or 10 minutes at 56 degrees C.