The statistical uncertainties associated with time-averaged positron emission particle tracking (PEPT) measurements of the position, velocity and acceleration of a small tracer particle have been investigated. Experiments were undertaken using the ECAT 'EXACT3D' PET scanner recently installed at the facilities of PEPT Cape Town at iThemba LABS, South Africa. Small "button" sources of (68)Ga were attached to the outer shell of a small mill and PEPT data were recorded over several half-lives, for the cases of the mill being empty and entirely filled with steel balls. The effect of tracer activity on the statistical uncertainties in the positions, velocities and accelerations derived from the measurements was investigated, as a first step towards fully quantifying the uncertainties associated with tracking particles via PEPT in laboratory-scale tumbling mills. (C) 2010 Elsevier Ltd. All rights reserved.