The interactions between M-CAT binding factors (MCBFs) in nuclear extracts from developing chick tissues with oligonucleotides containing CATTCCT or CATTGCT core sequence were analyzed by gel retardation and Southwestern blot. Gel retardation assays showed that binding activities of MCBFs expressed in all tested organs, including skeletal muscle, cardiac muscle, gizzard, liver and brain, whereas the binding patterns were different between five tissues. Also, the binding patterns of CATTCCT and CATTGCT core sequence-containing oligonucleotides respectively with MCBFs in skeletal muscle extracts were different from each other. Southwestern blot analysis indicated that a 30 ku MCBF existed in the extracts from five tissues of chicken embryos by using oligonucleotides containing either CATTCCT or CATTGCT core sequence as a probe, suggesting that 30 ku molecule is an ubiquitous factor expressed in all tissues and this molecule can bind to both oligonucleotides in the manner of monomer or/and dimer and polymer. These imply that 30 ku molecule is essential for MCBF binding activities. Besides the ubiquitous factor, the possibility of specific factor(s) interacting with 30 ku molecule to form a heterodimer to bind to DNA can not be excluded. The ubiquitous factor of 30 ku expressed in skeletal muscle during embryonic development and disappeared after birth.