There continues to be marked variation in rates of early retirement due to ill-health within and between organizations that warrants further investigation. The general and specific guidance that appears as an appendix in Supplementary data to this paper should help occupational physicians to make equitable recommendations when assessing applications for early retirement benefits and fitness to work.

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better to an intravenous regimen. We can only record, anecdotally, that he showed a complete recovery without neurological deficit.We have not obtained significant blood pressure reduction over two hours in severe hypertension with 80 mg propranolol or 100 mg atenolol by mouth, and bradycardia may be troublesome with these drugs. Further Lastly, it may be noted from studies on individual smokers that there are indications that the majority of smokers can adjust to a cigarette delivering less nicotine.:' That is, while many smokers changing to a cigarette delivering less nicotine tend to smoke so as to obtain more nicotine, it has been found that the total nicotine obtained, as estimated from their mouth-level exposure, is still generally considerably less than if they were to smoke their regular cigarette. Hence these and related observations suggest that it seems desirable to continue with the various measures, and also to consider additional measures, to make available cigarettes delivering less nicotine and tar. It is important to note that the "critical level" of serum lithium concentration, that at which sodium requirement exceeds sodium intake, consequently does not have a fixed value. When the sodium intake is low (diet, intercurrent infections) it may fall below the minimum requirement and the critical serum lithium concentration is consequently low in these circumstances. This means that intoxication may occasionally develop at serum lithium concentrations within the therapeutic range in the absence of kidney disease. In the case reported sodium intake and loss are not mentioned. Therefore the possibility remains that the patient had a low critical serum lithium level owing to low sodium intake. The reported serum lithium levels of 0-5-0-86 mmol/l (0 35-0-5 mg/100 ml) may support such a hypothesis if these levels reflect changes in serum lithium concentration on a constant dose, thus indicating an unstable condition. M E THOMPSON W F FORBESAnother and probably more reasonable explanation is the concurrent use of tetracycline. In clinical practice diarrhoea is a more common side effect of orally given tetracycline than the nephrotoxic effect. It is therefore possible that the tetracycline caused diarrhoea with concomitant increased sodium loss and that this increased the sodium requirement above the critical level and lithium intoxication developed as a consequence. Also a combination of the two mechanisms described here may have been at work.