Screening of hemorphins in extracts of rat lung, brain, heart and spleen was carried out. The threshold for detection of hemorphins was 0.01 nmol for spleen and 0.05 nmol for other tissues. Both the content and the composition of hemorphins differed significantly in the tissues analyzed. Heart and lung extracts were rich in these peptides, the content of the most abundant components reaching 16-44 nmol/g of tissue. In contrast, spleen and brain contained much lower amounts of hemorphins, i.e. about 0.3-2.6 nmol/g of tissue. The most represented hemorphin in lung, heart and brain was VV- hemorphin-5, while the content of other members of the hemorphin family depended significantly on the tissue analyzed: lung extract was also rich in LVV-hemorphin-5, heart contained similar amounts of LVV-hemorphin-7 and LVV- hemorphin-5 and brain of LVV-hemorphin-6. in contrast, the hemorphin family in spleen was represented mainly by C-terminally shortened VV-hemorphins, i.e. VV-hemorphin-4 and VV-hemorphin-3. The levels of hemorphins in all cases were sufficient to activate the opioid receptors of the respective tissues.