Experimental and clinical evidence support the assumption that eicosanoids affect the morphological development and the functional behaviour of the kidney during the intra-uterine and newborn periods. Inhibition of prostaglandin (PG) synthesis in the pregnant rhesus monkey resulted in renal hypoplasia in the offspring. The plasma levels of PGs are high in the newborn. Production of PGE2 by the cortical collecting duct was found to be similar in newborn and adult rabbit but the affinity of the renal tissue of the newborn for this eicosanoid was higher than that of the renal tissue of the adult rat. Based on findings in adult animals this would be expected to blunt the effect of antidiuretic hormone and account, in part, for the limited ability of the newborn to concentrate the urine. Yet, administration to unanaesthetized newborn rats of acetaminophen, a drug that inhibits the synthesis of PGE2 and thromboxane B2, blocked, rather than enhanced, the increment in urine osmolality produced by 1 h of water deprivation. The effect was absent in weaning and adult rats. A similar experimental manoeuvre increased sodium excretion in newborn but not in weaning or adult rats. Age-related differences are also evident with regard to side effects of PG synthesis inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)