Two instruments, namely the Aerosizer LD and the Particle Size Distribution Analyser (PSDA) 3603, were used to measure aerodynamic diameters of spray dried bovine serum albumin (BSA) particles with different surface corrugation (D-S). The measured aerodynamic diameters were compared with the values calculated using the theoretical model previously developed by our group. The model-calculated aerodynamic diameters have been shown to agree with the measured values for corrugated and less cohesive BSA particles with D-S varying between 2.18 and 2.41. For smoother and more cohesive BSA particles with D-S of 2.06 the measured and calculated values differed by 27% (compared to the value measured by PSDA 3603) and 115% (compare to the value measured by Aerosizer). This variation resulted from the difficulty to completely disperse the more cohesive particles during measurement. Hence, the model can be used to estimate aerodynamic diameter in situations when direct measurement fails due to unavailability of equipment, limitations or difficulty in dispersing powders into their individual particles in the aerosol. (c) 2008 Elsevier B.V. All rights reserved.