We have determined the DNase I sensitive chromatin domain of the lysozyme gene in the hen oviduct. When nuclei were digested with DNase I, about 14 kb of upstream and 6 kb of downstream sequences in addition to the 4 kb long transcribed region were preferentially degraded. The transcription start site is located near the center of the approximately 24 kb long sensitive domain. At the 3' boundary there is a rather abrupt transition from the DNase I sensitive to the resistant chromatin configuration whereas at the 5' border this transition occurs in a gradual fashion over 6-7 kb of DNA. No obvious correlation between the boundaries of the domain and repetitive sequences could be established. DNase I-hypersensitive sites are clustered within the boundaries of the sensitive domain which seems to represent a functional unit of the gene.