Ripening activity of seven candidate materials was examined in sugarcane plantlets propagated by sand culture. Test compounds included Polaris and CP 70139 (Monsanto), RH 1622 and C-9550 (Rohm and Haas), JF 4380 (ICI, Plant Protection Ltd.), PP 757 (ICI United States, Inc.), and Ripenthol (Pennwalt). Polaris served also as a standard ripener. All materials were administered as aqueous foliar sprays containing 3000 p/m active ingredient. Activity parameters included net growth (total green weight), sucrose content, and the enzymes acid invertase, acid phosphatase, ATP-ase, beta-amylase, and trehalase. CP 70139 activity surpassed that of Polaris while PP 757 equalled or moderately exceeded Polaris. Other compounds were relatively inactive. The significance of plantlet screening is discussed in terms of diminishing resources for ripener research, field problems to be solved by chemical means, and physiological requirements of candidate materials at the regional level.