The presence of melatonin, a known animal hormone, has been confirmed in many evolutionary distant organisms, including higher plants. It is known that melatonin increases tolerance to stress factors as a wide spectrum antioxidant. Tolerant genotypes have generally higher melatonin content than sensitive ones, and exposure to stressful conditions is known to increase endogenous melatonin levels. However, endogenous melatonin levels in seeds have never been used to select genotypes tolerant to abiotic stresses. Thus, in this study, the existence of possible relationship between seed melatonin levels of 28 pepper (Capsicum annuum L.) genotypes and their germination and emergence performance under chilling conditions (15 degrees C) was investigated. The results indicated that these parameters were much better for pepper genotypes with higher seed melatonin contents while those having less than 2 ng g(-1) additionally exhibited elevated levels of MDA and H2O2 but lower antioxidant enzyme activities. Thus, a positive relationship between seed melatonin content and chilling stress tolerance has been shown, suggesting a possible use of endogenous melatonin levels as a criterion in selecting chilling stress tolerant varieties. To save considerable time, money and labour, it is recommended that genotypes with lower melatonin contents are excluded from breeding programmes that aim to develop new stress tolerant genotypes.