Guard cell chloroplast numbers were counted in the tamarillo (Cyphomandra betacea (Cav.) Sendt.), the pepino (Solanum muricatum Ait.), and in wild relatives and polyploids of these species. Chloroplast number was found to be a reliable indicator of the euploid level in both species, but in aneuploids the effects of different chromosomes were variable. Some had no effect but in others the effects werepositive and sometimes significantly different from the diploids. Comparison of DNA amounts and plastid numbers in wild Cyphomandra species did not reveal a high correlation between these two characters. These results argue against a purely nucleotypic control of chloroplast number in guard cells in favour of a more complex genotypic system.