In most eukaryotic organisms, recombination events leading to exchanges between homologous chromosomes link the homologs in a manner that allows their proper attachment to the meiotic spindle. In the yeast Saccharomyces cerevisiae these exchanges are initiated in early prophase as double-strand breaks in the DNA. These breaks are processed through a series of intermediates to yield mature crossovers late in prophase. The following experiments were designed to monitor the appearance of the earliest recombinant DNA strands formed in this process. A polymerase chain reaction assay was devised that allows the detection of recombinant strands at a known initiation site for meiotic recombination. The time and rate of appearance of recombinant strands was found to coincide with commitment to recombination, demonstrating that DNA strands bearing sequences from both parental chromosomes are rapidly formed after the initiation of meiotic recombination.