The effect of pregnancy on kidney function was studied in 29 pregnancies of 17 patients with familial Mediterranean fever (FMF) and amyloidosis. Pregnancy associated deterioration of renal function occurred in seven patients who had advanced renal disease at conception, marked by serum creatinine > or = 1.5 mg/dl or urine protein > or = 2 g/24 h. This finding suggests that the severity of renal disease at conception may predict the fate of kidney function during pregnancy and puerperium.