Technical Abstract: Most research on the potential benefits of plant diversity, including increased production and resistance to stress, has been carried out in ungrazed areas. Very little information is available on plant species diversity in the pastures of the northeastern United States, and even less on seasonal patterns of plant diversity. To help remedy this lack of information, and as a first step towards understanding whether plant diversity provides benefits to graziers, we sampled the pasture plant communities on five farms, two in eastern New York (NY1, NY2), two in eastern Pennsylvania (PA1, PA2), and one in Maryland (MD1). We found 189 species on these five farms in two years of seasonal sampling (spring, summer, fall in 2004-2005). Nearly half of these plant species were found in fewer than 5% of the samples. Although there were differences in species richness among farms and pastures, and across seasons, those differences didn't translate into less bare ground showing, even during the summer when conditions are driest. This simple measure of plant diversity may not be a good indicator of the benefits that can be provided by a diverse mixture of forage species.