The proton microprobe at Heidelberg was used to measure the intracellular calcium distribution in two tip growing plant cells, the pollen tube of Lilium longiflorum and the protonema tip cell of the moss, Funaria hygrometrica. The cells were either chemically fixed with glutaraldehyde and air dried or frozen in melting nitrogen and freeze dried. Some samples were additionally pretreated with calcium interacting drugs. The specimens were measured with a proton beam of 3 MeV, focused to a point for X-ray spectra or to a line for scanning analysis. Thereby the cells were moved automatically step by step along the beam, in order to measure profiles of elemental distribution. Independent of the fixation technique the cells revealed a higher calcium content at their tips as compared to the base. The shape of the calcium distribution however depended strongly on the fixation technique. The calcium interacting drugs additionally influenced in different ways the content and distribution of cellular calcium. The results confirm the postulated tip-to-base calcium gradient in tip growing plant cells. Among other factors, calcium is assumed to regulate polar secretory processes that are required for tip growth.