Changes in inhibitor activity in the onion bulbs (Allium cepa L.) cv. Sochaczewska during storage were investigated. Onions were dried under an umbrella roof until October 15th or November 15th and thereafter stored in a cold-room at 0 - 1°C until May 15th. The activity of inhibitors fluctuated markedly during the storage period. At least two peaks and two decreases of inhibitor activity were observed. The weather conditions seemed to strongly influence the level and the date of appearance of inhibitors in onions. Higher inhibitor activity is usually connected with better storage and less sprouting of onions during storage. Prolonged drying under an umbrella roof enhanced onion quality after storage only in these cases when it actually improved the drying of onions.