The swimming behaviour of iron-fed and control cells was analyzed under terrestrial and hy pergravity conditions. Acceleration dependent sedimentation rates were determined to study the relationship between acceleration and gravikinesis. Iron-fed cells showed increased sedimentation rates as compared to control cells. Iron-ingestion results in an increase of the cytoplasmatic density. We conclude that in iron-fed cells gravikinesis increased with acceleration, whereas gravikinesis slightly decreased in control cells.