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A method is described for the determination of residue levels of sulfadimethoxine in animal tissues. The sulfonamide is extracted from the tissues with chloroform, partitioned into dilute ammonia, and reacted in the Bratton-Marshall procedure. The dye formed is extracted into «-butanol prior to colorimetry. As little as 0.1 p.p.m. of sulfadime-thoxine was accurately determined in this fashion on a 10-gram tissue sample. Average recovery for all tissues ranged from 70 to 90%. Nonspecific Bratton-Marshall color of untreated control tissues is kept below 0.05 p.p.m. of apparent sulfonamide. As little as 1.0 /xg. of sulfadimethoxine can be measured accurately.

Thirty-six substituted phenyl 2-propynyl ethers and thioethers were tested for synergistic activity toward carbaryl in the housefly. The most active compounds, namely the 2,3,6-trichloro, 2,4-dibromo, 2-nitro, 3-nitro, and 2-nitro-4-chlorophenyl 2propynyl ethers lowered the LD50 for carbaryl to less than 0.1 ag per fly. Substitution with more than one nitro group or more than three halogens decreased activity, as did the introduction of an alkyl, alkoxy, or aryl group or the formation of a thioether.

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