Abstract: Retractable marker pens and ink formulations for marker pens. The ink formulation has particular utility as a fluorescent ink for highlighting text or print. The formulation reduces the rate of ink evaporation from conventional felt, fiber or plastic marker tips. This property makes the ink especially suitable for use in retractable marker pens which do not normally employ a separate tight fitting cap or a lint guard to protect the marker tip from ink evaporation when the marker pen is in non-use. The ink formulation exhibits excellent flow characteristics to conventional felt, fiber or plastic marker tips over a wide range in tip widths. The ink does not leak from the tip and does not penetrate paper so as to obscure text or printed material on the opposite side of the paper. The ink is composed of a fluorescent dye, selected from methine, xanthene and anthraquinone dyes dissolved in a multicomponent solvent system.