Two groups of beef cattle, consisting of two steers and one cow per group, received a total dose of 300 mg. of p,p'-DDT per kg. of body weight over either a 3or 30-day period. One steer from each group was sacrificed before a 7-week depletion period which followed the treatments. The remaining animals were sacrificed at the end of 7 weeks of de-pletion. Total DDT residues (DDT, DDD, and DDE) appeared on the average to be evenly dis-tributed throughout the extractable fat of beef cattle, based on samples of 13 different tissues. Differences were found in the total DDT residue content of extractable fat due to dose rate (P < 0.01) and time after treatment (P < 0.01), and the relative amounts of DDT, DDD, and DDE were different (P < 0.05) between depot fat, muscle, blood, and milk fat.

A rapid and sensitive method of analysis in which high-speed liquid chromatography was used with ultraviolet absorption detection was developed for determining residues of Thompson- Hayward TH 6040 (N-(4-chlorophenyl)-N'- (2,6-dinuorobenzoyl)urea) in cows' milk. The larvicide is extracted from whole milk with ethyl acetate, and the lipids are removed by partitioning between hexane and acetonitrile. After evaporation of the acetonitrile, the residue is dissolved in ethanol, and aliquots are injected into a liquid chromatograph, using methanol-water (1+1) as the mobile phase in a packed column. Recovery of TH 6040 from cows' milk is essentially quantitative, and no interfering substances appear on the chromatogram. The lowest detectable level was 10 ng. Milk from a cow fed 1 mg larvicide/kg body weight daily in the diet was analyzed by this procedure, and no detectable residues (&lt;0.1 ppm) were found over a 15 week sampling interval.

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