CYTOLOGICAL descriptions of meiosis have long been a staple of biology textbooks, but a biochemical account of the process with a comparable claim to universality has been unavailable. We present here evidence for a common pattern of DNA metabolism in male meiotic cells of lilies and rodents during the zygotene-pachytene stages when crossing-over is presumed to occur. The prevalence of a common pattern between species that are as phylogenetically distant as lily and mouse has led us to conclude that the organisation for meiotic crossing-over in at least higher eukaryotes is probably universal in distribution. Four components of the pattern have been identified in separate studies of lilies, mice and rats, most of which have been or are being published elsewhere1-3: the transient appearance of a protein (`R-protein') that facilitates DNA reannealing; the programmed introduction of single strand nicks on completion or near completion of chromosome pairing; the repair of endogenously formed nicks and gaps either immediately following or overlapping the interval of nicking; the preferential localisation of gaps and nicks in specific DNA sequences.