Chimeric genes for expression of a foreign gene in the Chlamydomonas reinhardtii chloroplast were constructed. These chimeric genes are composed of the promoter from chloroplast genes, rbcL, psbA, and atpA, 5'- and 3'-untranslated regions, and the Escherichia coli beta-glucuronidase (GUS) structural gene (uidA) as a foreign gene. Three types of chloroplast transformants (RG, PG, and AG), which contained the rbcL-uidA, psbA-uidA, and atpA-uidA chimeric genes integrated in the chloroplast genome, were generated by particle bombardment. The AG transformant grown under photoautotrophic conditions showed the highest GUS activity (130 nmol/min/mg protein) so far reported in C. reinhardtii, and the accumulated GUS protein accounted for 0.08% of the total soluble proteins. GUS activity in RG was 12% of that in AG, and no activity was detected in PG. We also measured the GUS activity from transformants grown under heterotrophic conditions, but the culture conditions made little difference in activity levels. The difference in the amount of accumulated GUS protein in the transformants was paralleled by the difference in the level of transcripts, and the pattern of gene expression was not the same as that of the endogenous genes in the chloroplast.