I compare the informational efficiencies of contingent rating, contingent ranking, and two contingent paired-comparison methods as alternatives to the referendum contingent valuation method. The contingent rating method is hypothesized to be most efficient because ratings convey information on preference intensities and can uniquely represent respondent indifference or ambivalence. Survey data on hunters' ratings of alternative hypothetical hunting trips are used to estimate four alternative indirect utility models from which marginal willingness-to-pay measures for individual trip attributes are derived. Model compa¡ WTP estimates, and their confidence intervals confirm the relative efficiency of the contingent rating approach.

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The active forms of 6-(p-hydroxyphenylazo)-uracil and 6-(p-hydroxyphenylazo)-isocytosine were isolated and identified as their respective hydrazino derivatives. These arylhydrazino pyrimidines selectively inhibited a chromatographically distinct DNA polymerase from Bacillus subtilis. The actions of the reduced drugs on this polymerase were identical to those observed on ATPdependent DNA synthesis in toluene-treated cells; dGTP competitively antagonized the inhibitory activity of the uracil derivative, and dATP competitively antagonized that of the isocytosine derivative. Analysis of the interactions of the arylhydrazinopyrimidines and nucleic acid bases by nuclear magnetic resonance suggested that hydroxyphenylhydrazino-uracil and hydroxyphenylhydrazino-isocytosine pair in a novel manner with, respectively, cytosine and thymine. A mechanism of inhibitor action, involving binding of the reduced drugs to enzyme and the pyrimidines of DNA template, is proposed.The arylazopyrimidines, 6-(p-hydroxyphenylazo)-uracil (HPUra) and 6-(p-hydroxyphenylazo(-2-amino,4-keto-pyrimidine (HPIsocytosine), selectively inhibit the semiconservative replication of DNA of Bacillus subtilis by inhibiting the function of a specific DNA polymerase (1-3). It now seems clear that these arylazopyrimidines do not inhibit DNA synthesis in drug-sensitive systems unless they are first reduced, either by metabolism, for toluene-treated cells (4, 5) or chemically, for cell-free preparations (2, 3). In this paper we present evidence that the active, reduced forms of HPUra and HPIsocytosine are their respective hydrazino derivatives. We also propose, on the basis of an analysis of novel base-pairing properties of these compounds and an examination of their action on a distinct DNA polymerase of B. subtilis, a mechanism of action that can account for their ability to antagonize the function of purine deoxyribonucleotides as substrates in replicative DNA synthesis (5). MATERIALS AND METHODSChemicals. 6-(Hydrazino)-uracil and arylazopyrimidines were generously provided by Dr. Bernard Langley of the Imperial Chemical Industries, Ltd. HPUra, HPIsocytosine, and 6-(phenylazo)-uracil (PUra) were purified by chromatography on silicic acid (6). [ of input radioactivity, was applied to a column (0.65 X 6.5 cm; 2-ml bed volume) of DEAE-Sephadex (Pharmacia; A-25; HCO3-form) that had been washed with 20 volumes of 5 mM triethylammonium bicarbonate buffer (pH 5.5) thoroughly purged with gaseous CO2. The column was eluted with the same buffer at a rate of 0.25 ml/min, and twenty 1-ml fractions were collected. The elution buffer then was changed to 1 M triethylammonium bicarbonate (pH 7.7), and 15 more fractions were collected. This method of elution resulted in the quantitative recovery of radioactivity applied to the column. One-half ml of each fraction was applied to 25-mm glass-fiber discs, which were dried at 800 and counted by liquid scintillation sl)ectrometry.Preparation and Reduction of Arylazopyrimidines. 2 ml of a fresh 1 M solution of sodium dith...