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Replication times for all important chromosome bands, of both types R and Q (277 structures) are analysed. — The R-bands form a group of structures whose DNA replicates during the early S-phase, while the DNA situated in the Q-bands replicates during the late S-phase. — There may not exist overlapping between replication times of these two types of structures. — The widest R-bands are those which are the earliest to replicate; in general, the most intense Q-bands are those which are the latest to replicate. Especially among these last ones, a certain asynchronism exists between the replication times. Finally the heterochromatin of chromosomes 1, 16 and Y and of the short arms of the acrocentrics could contain two types of DNA which replicate at different times.