A multichannel measuring system MMS-05 for continuous and synchronized profile monitoring of the CO2 concentration in cultivation installations is described. The system guarantees the performance of vertical and horizontal gradient measurements and registration of CO2 concentration in a green- house. Experimental studies with 6 cultivars of greenhouse tomato plants performed for testing the system show that the fluctuations in CO2-profiles, and respectively the CO2 concentration in the greenhouse, follow a time dependant pattern with a pronounced decrease during the midday hours 10 a.m. ÷ 6 p.m. when CO2 con- centration reaches 160 ÷ 180 mmol mol–1. During the night, as a result of plant and soil respiration, the CO2 concentration rises to 450 ÷ 500 mmol CO2 mol–1.