A sensitive and specific radioimmunoassay for measuring urinary kinins was developed. Antibodies against bradykinin were induced in rabbits by injecting bradykinin coupled to bovine albumin. One of the antisera generated was used at a final dilution of 1:18,000 to obtain a 30% total binding of bradykinin-(8-tyrosine)-[<sup>125</sup>I]-triacetate. Synthetic bradykinin (5–1,000 pg) was used as standard in the curves. The sensitivity of the assay was 5 pg. The recovery of bradykinin added to urinary samples was 86.85 ± 6%. The intraassay and interassay coefficients of variation were 3.3% (n = 12) and 4.4% (n = 5), respectively. The antiserum showed no cross-reactivity with oxytocin or low molecular weight kininogen and cross-reacted with kallidin (lys-bradykinin), met-kallidin, and angiotensin I, but cross-reaction with angiotensin I (2.5%) was low enough to be disregarded. The mean urinary levels of total kinins in 12 normal subjects were 23.2 ± (SEM) 2.2 µg/day.