Intact and excised cultured pea roots (Pisum sativum L. cv Alaska) were treated with chlorsulfuron at concentrations ranging from 2.8 ×10−4 M to 2.8×10−6 M. At all concentrations this chemical was demonstrated to inhibit the progression of cells from G2 to mitosis (M) and secondarily from G1 to DNA synthesis (S). The S and M phases were not directly affected, but the transition steps into those phases were inhibited. Total protein synthesis was unaffected by treatment of intact roots with 2.8×10−6 M chlorsulfuron. RNA synthesis was inhibited by 43% over a 24-h treatment period. It is hypothesized that chlorsulfuron inhibits cell cycle progression by blocking the G2 and G1 transition points through inhibition of cell cycle specific RNA synthesis.