Previous studies have analyzed collection efficiencies and reaerosolization rates of liquid-based bioaerosol collectors. However, these studies. did not analyze latent internal losses in the samplers, i.e., the fraction of the particles that is aerosolized from the collection liquid, attach to the samplers' inner surfaces and do not leave the sampler via outlet. Here, we investigated the internal losses and reaerosolization rates in BioSampler (SKC Inc., Eighty Four, PA) and AGI-30 (Ace Glass Inc., Vineland, NJ) bioaerosol collectors operated with different amounts of liquid as a function of particle type (polystyrene latex particles of 0.9 and 3.2 mu m, B. subtilis bacteria and C. cladosporioides fungal spores), particle concentration ("low" and "high" differing by a factor of 100) and operating time (15 and 30 min). The samplers were filled with sterile deionized water containing known (reference) particle concentrations and were operated in a particle-free atmosphere for 15 or 30 min. The overall particle loss was determined by comparing the concentration of particles remaining in the collection liquid with the reference concentration. The reaerosolization rates were estimated by comparing the concentration of particles collected at each sampler's outlet with the reference concentration. The internal loss was determined as a fraction of particles remaining attached to the inner walls of a sampler, i.e., particles not in the collection liquid and not reaerosolized. All the investigated variables had a statistically significant effect on the overall particle loss, the reaerosolization rate and the internal loss. Averaged for all test conditions, the internal loss for BioSampler with 5 mL liquid, BioSampler with 20 mL liquid and AGI-30 was 37.7%, 29.6% and 22.5%, respectively. The observed reaerosolization rates were rather low and ranged from 0.2% to 6.9%. This study shows that depending on a particular set of sampling conditions a substantial fraction of already collected particles could leave the collection fluid, attach to the inner surfaces of the samplers and not be available for sample analysis thus affecting the accuracy of bioaerosol investigations. (C) 2011 Elsevier Ltd. All rights reserved.