In an attempt to establish a model of chlamydial ascending salpingitis and infertility, three inbred strains of mice, C3H/HeN (H-2(k)), C57Bl/6N (H-2(b)), and BALB/cAnN (H-2(d)), were inoculated intravaginally with 3 X 10(7) inclusion-forming units of the Chlamydia trachomatis mouse pneumonitis biovar, Mice mated 6 weeks following inoculation were found to have a significant decrease in fertility rate compared with the control groups, as shown by a reduction in the number of pregnant mice and a decrease in the number of embryos.