Whereas polyploidy has been found in more than half the Gramineae, the occurrence of 2n gametes, a potentially major mechanism of polyploid production, has been rarely studied. In the present work, the frequency of 2n egg production in nine diploid (n = 2x = 14) subspecies of the polyploid complex Dactylis glomerata has been estimated by determining the ploidy level of the progeny in 98 2X-4X crosses. The 2n egg origin of the 4X offspring was verified using enzyme markers. The frequency of 2n egg production in each subspecies was estimated from the number of 4X offspring, the number of florets in the seed plant and the fertility of the subspecies. The ploidy level of the progeny was determined by chromosome counts or nuclear DNA quantification using flow cytometry. Plants producing 2n eggs were detected in 47% of the fertile crosses, involving eight subspecies. Variability was related to individuals and not to subspecies. Average 2n egg frequency was 0·49% for all crosses, and 1·53% for crosses where 2n egg production was detected. Individual frequencies did not exceed 3·5%, with the exception of 26% in one plant. Triploid block was higher and fertility, frequency of high 2n gamete producers and average 2n gamete frequency were lower in the 2X-4X crosses than in the opposite 4X-2X crosses involving the same plants, previously studied. Diplogynous and diplandrous gamete production were not correlated with each other. However, the widespread occurrence of plants producing both kinds of 2n gametes in almost all the studied subspecies, as well as the presence of several individuals able to produce high rates of 2n eggs or 2n pollen, support the hypothesis that tetraploids can be formed anywhere and anytime by sexual polyploidization in diploid populations of Dactylis glomerata L.