During a cytogenetic survey of boys admitted to the allocation centre for Scottish Borstals a physically normal 18-year-old boy was found to have an apparently balanced translocation between a chromosome number one and a chromosome in group C. In the course of cytogenetic investigations on the relatives of the propositus it was noted that an unusually large secondary constriction in a chromosome number one and a Robertsonian translocation between two D group chromosomes were also segregating in the family. Other studies undertaken on all the available members of the family included the examination of red cell antigens and genetically determined enzyme systems, and of serum proteins. The segregation of the chromosome markers will be discussed and also the information obtained about the relation of the genetic loci to the chromosomes involved.