Intraspecific genome size variation has been well documented in Zea mays L. Two of the major reasons that intraspecific genome size variation is widely accepted in maize are: 1) the large amount of the variation (37%+) and 2) the amount of knob DNA sequence is associated with much of the variation. Interestingly the large amount of genome size variation seems restricted to between different types of maize lines. When observing within types of maize i.e. flint, flour, corn belt hybrids, the amount of genome size variation falls dramatically. The purpose of this study was to document genome size variation in popcorn germplasm and to determine if knob sequences fluctuate with varying genome sizes. Several popcorn plant introduction lines were obtained from the USDA, ARS, NCRPIS Regional Plant Introduction Station at Iowa State University, Ames, Iowa. Flow cytometric analyses were conducted and significant nuclear DNA content variation was observed among these lines. The amount of variation was much less that the 37% variation found among maize types. Root tip squashes were prepared from the popcorn plant introductions. Primed In situ labeling (PRINS), using a degenerate knob primer sequence, was used to reveal the number, size and location of chromosomal regions containing the knob sequence. Associations between genome size and knob sequences in popcorn germplasm will be presented and evolutionary implications discussed.