A hand-held, multi-channel pipettor has an electronically controlled motor to reposition pipette tips for different center to center spacing. Each repositionable tip fitting assembly has a cam following pin that is driven by cam tracks in a motor driven roller drum. Stationary ports for the multiple aspiration cylinders are strategically placed to simplify management of flexible tubes leading to the repositionable pipette tip fitting assemblies. The pipettor has a user interface that can be operated conveniently by one hand to reposition pipette tips. It has a pipette tip ejection mechanism with a sinusoidal stripper bar.