Telomeric restriction fragments were genetically mapped to a previously described linkage map of Magnaporthe grisea, using RFLPs identified by a synthetic probe. (TTAGGG)3. Frequent rearrangement of telomeric sequences was observed in progeny isolates creating a potential for misinterpretation of data. Therefore a consensus segregation data set used to minimize mapping errors. TWelve of the 14 telomeres were found to be genetically linked to existing RFLP markers. Second-dimensional electrophoresis of restricted chromosomes confirmed these linkage assignments and revealed the chromosomal location of the two unlinked telomeres. We were thus able to assign all 14 M. grisea telomeres to their respective chromosome ends. The Achilles' cleavage (AC) technique was employed to determine that chromosome 1 markers 11 and CH5-120H were approximately 1.8 Mb and 1.28 Mb, respectively, from their nearest telomeres. RecA-AC was also used to determine that unlinked telomere 6 was approximately 530 kb from marker CH5-176H in strain 2539 and 580 kb in Guy11. These experiments indicated that large portions of some chromosome ends are unrepresented by genetic markers and provided estimates of the relationship of genetic to physical distance in these regions of the genome.