The combination of heat and the dependent position, as experienced with a standard lower extremity whirlpool treatment, has the potential of encouraging lower extremity swelling. This study examined the effects of whirlpool and the dependent position on lower extremity swelling in 40 healthy physical therapy students and therapists (12 males, 28 females) between the ages of 20 and 40 (= 24.3 yrs). Volumetric measurements were taken before and after three experimental conditions. Condition number one involved a 20-minute treatment in a leg whirlpool at 40 degrees C (104 degrees F). The second condition involved sitting for 20 minutes with the foot resting on the bottom of an empty leg whirlpool. The third condition involved a 20-minute rest in the supine position. A one-way ANOVA and Tukey's post hoc test were used to analyze the data. Analysis revealed the greatest increase in limb volume following the whirlpool treatment (= 44 ml +/- 30.5). The second greatest increase (= 20.5 ml +/- 32.5) occurred when the extremity was maintained in the dependent position. When placed in the supine position, subjects experienced a decrease in limb volume (= -16 ml +/- 15.2). The findings were statistically significant at the 0.01 level. The results indicated that while lower extremity swelling does occur from treatment in a whirlpool or by placing the extremity in a dependent position, the changes seen are not as dramatic as those reported in the upper extremity. The variation is hypothesized to be due to physiological and anatomical differences between the upper and lower extremities. Caution is advised, however, when using whirlpool to treat lower extremity injuries in the presence of significant musculoskeletal or vascular pathology because marked swelling could result. J Orthop Sports Phys Ther 1992;16(4):169-173.