Premise of research. Self-incompatibility (SI) is a frequent mechanism of plants to avoid self-pollination. Pollen esterases (EC 3.1.1.-) play an important role in pollination by enabling the penetration of pollen tubes through the cutin layer (cutinases). Therefore, their composition could contribute to SI. To test this hypothesis, esterase activity and isozyme profiles between self-compatible and self-incompatible chamomile plants (Matricaria chamomilla L., Asteraceae) were compared. Methodology. Stable self-incompatible plants were selected, and the approximate number of alleles contributing to SI were determined in a full-diallel cross. Esterase activity of self-compatible and self-incompatible chamomile plants was tested on the four substrates that follow: 1-naphthyl acetate, 2-naphthyl acetate, 1-formyl-2-naphthyl acetate, and indoxyl acetate. Esterases were characterized by electrophoretic methods, both concerning protein size and isozyme pattern in two different buffer systems. Pivotal results. Seventeen percent of all plants analyzed were self-incompatible. Eight self-incompatible plants-crossed in a full diallel-showed six different alleles responsible for SI, a number that can only be regarded as a minimum number of alleles due to the low sample size. Self-incompatible plants showed a significantly lower esterase activity for the two substrates, namely, 1-naphthyl acetate and 2-naphthyl acetate. With 1-formyl-2-naphthylacetate, however, esterase activity of self-incompatible plants was higher than that of self-compatible plants. With indoxyl acetate, no significant difference between self-incompatible and self-compatible plants could be found. The different esterase isozyme patterns observed did not correlate to the compatibility mechanism. Conclusions. The composition of pollen esterases is variable and could contribute to SI by differences in their substrate specificity.