SUMMARY.— Surface lipids were removed from anaesthetized rats by dipping them into lipid solvent up to the neck. After varying time intervals, the lipid which had accumulated was removed and assayed gravimetrically. The accumulation of lipid was linearly related to time up until the fourth day, after which it decreased. Passive accumulation from a reservoir of lipid was excluded by the finding that the amount of lipid extracted at 7 successive 4‐day intervals did not decrease. The lipid accumulation during the first hours after solvent extraction was too rapid to be accounted for by lipid originating from growth of hair and epidermis. It was concluded that sebum secretion was measured and the rate during the first 4 days was 13·3 ± 0·4 mg./100 G. body weight.

Summary Acetylcholinesterase (AChE) activity in amniotic fluid was assayed directly by a reaction rate method at 30°C using acetylthiocholine iodide as substrate and ethopropazine as a safe ‘pseudo’ cholinesterase inhibitor. Fresh samples from 101 normal pregnancies of 14–24 weeks gestation had a mean AChE activity of 2.56 u/1 (SD 1.10). Elevated levels of AChE were found in association with open spina bifida (5.5–20.4 u/1), anencephaly (10‐2‐19‐5 u/1), exomphalos (2.7–15.6 u/1), intrauterine death (30.2–59.3 u/1) and Turner's syndrome (36.4 u/1) but not with closed spina bifida or rhesus isoimmunisation. When AChE activity was expressed as a percentage of the total cholinesterase activity (‘percentage AChE’), there was a good correlation between AChE activity and‘percentage AChE’in normal pregnancies and the values associated with the 37 pregnancies affected by open neural tube defects (NTD) fell outside the 99.9 per cent confidence limits of the normal group. Qualitative differences in cholinesterase activity could be demonstrated between the groups with exomphalos and open NTD. It is suggested that the assay might be used satisfactorily to demonstrate the presence of open NTD in affected pregnancies.

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The Bioassay ofAndrogens and Anti-androgens Using Sebum Secretion in the Rat This communication is concerned with two simple points:(1) The potency of an androgen and the efficacy of anti-androgen must be defined in relationship to the bioassay system used. The terms androgen and anti-androgen are a confusing over-simplification of a number of heterogeneous biological properties.(2) The response of the rat sebaceous gland provides an important new bioassay for androgen and anti-androgen (Archibald & Shuster 1967).