ISOLATED chloroplast preparations offer great advantages in the analysis of carbon pathways of photosynthesis because the system is not complicated by non-chloroplast metabolism, and kinetic analyses1 can be made which are difficult with whole leaves2. Unfortunately the slow diffusion and equilibration of CO2, HCO−3 and CO2−3 in the suspension medium is a serious disadvantage in gas exchange or 14CO2-12CO2 pulse-chase experiments3, but this difficulty can be overcome by using a thin film of concentrated chloroplast suspension spread on a non-absorbent support in the form of an “artificial leaf”. Recent experiments by Coombs and Baldry have shown that pea and spinach chloroplast preparations supported on filter paper were stable only for periods of up to 10 min4. We have used Acetabularia mediterranea Chloroplasts on filter paper to analyse the products of short term (1 s to 5 min) 14CO2 fixation, but we found them insufficiently stable for longer experiments or gas exchange measurements. We have overcome this difficulty, however, by supporting Chloroplasts on a non-absorbent grid instead of filter paper.