To identify a specific heterozygote advantage in familial Mediterranean fever (FMF), responsible for the high carrier rate of 1/6 in North African Jews, we studied the morbidity and mortality of 148 parents of affected patients and of 148 ethnically matched control persons. Our data demonstrate an apparently reduced prevalence of asthma in the heterozygotes compared with the control persons (3 vs. 6). There were no significant differences between the 2 groups in fertility rate, number of pregnancies and deliveries, or the prevalence of common diseases. Our data are in agreement with previous studies which demonstrated decreased asthma prevalence in FMF patients. It further confirmed, these findings suggest that identification of the FMF gene on 16p may provide an insight into asthma.