AbstractA technique is described for the automatic recording of the uptake of pesticides and related compounds by viable, small organisms suspended in aqueous solution. The relation of time to uptake thus determined allows the study of the kinetics and the characterisation of the uptake processes.The technique is based on a recycling of the incubation vessel fluid, obtained by a simple filtration process, through the flow cell of a spectrophotometer. The rate of uptake of compounds, which need to have sufficient absorption in the visible and u.v. region, is followed spectrophotometrically by repetitive measurement of spectra or of absorbance values at a single wavelength. Uptake processes are studied under controlled conditions of temperature and atmosphere. The method has proved to be applicable to yeast cells, fungal spores, nematodes, insect eggs and algae, so that it can be used to good advantage in pesticide research.However, the technique is not suitable for very small organisms such as bacteria and for easily deformable cells, e.g. erythrocytes.The utility of the method has been demonstrated in the uptake of 2‐chloro‐6‐phenylpyridine by nematodal larvae (Anguina tritici) which sorb the compound reversibly, and in the uptake of 4,5‐dichloro‐2‐nitrobenzonitrile by fungal spores (Fusarium culmorum) which is converted into the corresponding amino compound. These examples illustrate that the technique is very useful for the study of uptake processes which can be interpreted in terms of accumulation or convers