Three farrowing rooms, each housing 5 sows and litters, were used to study the effects of floor applied mineral oil on dust concentrations (>0.5 mu m diameter). Rooms were ventilated at a similar rate (266 L/s). Three treatments were considered over a 3 week duration: oil was applied on day 8, 15, and 22; oil was applied only on day 8; and no oil was applied. Oil applied to pen floors at a rate of 24 mL/m(2) using a low pressure hand sprayer was found to be effective. Dust concentrations (particles/mL), wet and dry bulb temperatures, ventilation rate, and total piglet mass per room were recorded on day 9, 16, and 23 in each treatment. At day 23, dust concentrations 24 h before measurement were 0.8 particles/mL, oil applied only on day 8 were 5.5 particles/mL, and the concentration when no oil was applied was 5.6 particles/mL. The greatest increase in dust concentration occurred between weeks 2 and 3 when growth rate of the piglets was most rapid. Applying oil 24 h before measurement resulted in an average dust reduction of 73%. At week 3, the respirable particle production rates were 5, 25, and 30 particles/s per pig for oil applied 24 h and 15 d before measurement and no oil application, respectively.