From 1948 to 1955, 2% chlordane residual sprays had been used successfully to control Rhipicephalus sanquineus in a large dog kennel in n. New Jersey, but in 1955 a large infestation developed which could not be controlled with chlordane. In the laboratory, these ticks withstood exposure to 2 to 10% chlordane residues. Malathion used as a residual spray at 1 and 2% concentrations gave partial control of these ticks, as did 1% malathion dips of dogs. Dusting dogs with 4% malathion and 1% lindane failed to give control. Lindane gave tick control when applied in the building as a residual spray at 0.25 or 0.5% concentration or applied to dogs as a dip containing 0.045% lindane.