K distribution in P. vulgaris twining shoots was studied using atomic absorption spectrophotometry and electron microprobe analysis. In the free-moving parts of the shoots, there was a longitudinal gradient of K content with a max. in the bending zone. Mechanical immobilization of the shoots for 6 or 24 h appeared to shift the max. level along the free-moving part. Moreover, the concave half of the bending zone contained more K than the convex half. The comparison between twining and immobilized shoots showed that changes in K distribution were directly related to the presence or absence of movement. It was further proposed that these ion movements were related to variations in the cell water content, as observed during circumnutation.