A sample of 60 natural populations of perennial ryegrass from France has been studied for allelic variation at 7 polymorphic enzyme loci . Population genetic statistics are of the same magnitude than those previously reported for other outbreeding, short-lived perennial species (P = 64%, A = 2 .75, H = 0 .270) .Genotype frequencies at most collection sites do not deviate significantly from Hardy-Weinberg expectations, with however a slight deficit of heterozygotes which may be accounted for by a Wahlund effect. Gene diversity is mainly explained by the within population component . The between population differentiation F s, averaged on 4 loci is only 0 .054, which accounts for only 6% of the whole diversity .When mapped, most allele frequencies do not show any special structure . Only five alleles present a clinal trend from North to South . These 5 alleles are probably related to some climatic factors such as average temperature or potential evapotranspiration . The causal hypotheses about the low level of betweenpopulation differentiation and spatial structure are discussed with reference to the literature .The consequences of the found population structure for sampling and conservation strategies of natural populations for genetic resources are presented and discussed .