The population genetic structure of white marlin (Tetrapturus albidus) was investigated with restriction fragment length polymorphism (RFLP) analysis of mitochondrial (mt) DNA.  The technique revealed substantial variation within samples of white marlin from the U.S. mid-Atlantic coast, Caribbean, southern Brazil and Morocco.   Collections of white marlin from the same geographic location taken in different years were not significantly heterogeneous, allowing temporal samples to be pooled for analyses of homogeneity among geographic locations.  The distributions of mtDNA haplotypes among relatively large samples (36-76 individuals) of white marlin from four sampling locations was not significantly different(p=0.06), although it was noted that the probability of homogeneity decreased as sample sizes increased.  At this time the null hypothesis of a total Atlantic stock of white marlin, a model which is also supported by observations on the distribution, spawning, and movements of the species, cannot be rejected.  However, there appear to be some restrictions to gene flow (exchange), with a greater impediment to gene flow across the Atlantic (east/west) than across the equator (north/south).