The ability of flowers and blossoms to convert biochemical substrates into volatile products is utilized for the development of biosensors using such plant tissues as catalytic components. It is shown that both minced and intact tissue portions from carnation and chrysanthemum flowers can be coupled with potentiometric ammonia gas sensing electrodes to prepare sensors for urea and some amino acids with good response properties. Surprisingly different response and selectivity patterns are found among species of flowers and for the structural subelements of a single type of flower.