Tetrahymena contains vertebrate hormone-like materials. The level of one of these, insulin increased during starvation in a previous experiment. We hypothesized that other hormones are also influenced by starvation. To prove the hypothesis Tetrahymena pyriformis cultures were (1) starved for 24 h; (2) starved for 24 h and re-fed for 30 min or (3) starved for 30 min. Amount and localization of vertebrate-like hormones, produced by Tetrahymena, β-endorphin, adrenocorticotropin (ACTH), serotonin, histamine, insulin and triiodothyronine (T3) were studied by immunocytochemical methods using flow cytometry and confocal microscopy. Long starvation elevated with 50% the hormone levels, while short starvation moderately elevated only the serotonin level in the cells. After short re-feeding endorphin and histamine returned to the basal level, ACTH and serotonin approached the basal level, however, remained significantly higher, while insulin and T3 stood at the starvation level. The results show that such a stress as long starvation provokes the enhanced production of hormones which likely needed for tolerating the life-threatening effect of stress.