We have examined 31 newchlorina mutants of barley using in vivo absorption spectroscopy, 77 K fluorescence emission spectroscopy, room temperature fluorescence induction kinetics, HPLC separation of pigments and SDS-PAGE. Based on these properties they can be placed into 4 groups. The first group consists of 10 mutants which are allelic to the chlorophyllb-lesschlorina-f2 and comprises five strongly and three slightly leaky mutants at this locus. The decrease in chlorophyllb content was correlated with a corresponding decrease in the amount of chlorophylla/b-proteins in the thylakoids. One mutant (chlorina 106) was found which had a very low chlorophyllb content and a deficiency in Chla/b-P2, but was not allelic tochlorina-f2. The second group ofchlorina, mutants has unusual fluorescence properties, with a high Fm/Fo ratio. Gaussian deconvolution of the 77 K fluorescence emission spectra revealed an increase in the amplitude of components emitting at 694 and 718 nm. The possibility is discussed that these properties result from the absence of the PSI connecting antenna LHCI-680. The third group has a Fs/Fo ratio <1, and other properties consistent with a partial deficiency in the chlorophylla-proteins of PSII reaction centres. The fourth group consists ofchlorina mutants which are very similar to wild-type in the properties examined, differing mainly in having a lower chlorophyll content.