Sirs,We read with great interest the study by Menon et al. regarding concentrations of serum 25-hydroxyvitamin D [25(OH)D; a measure of body stores of vitamin D] and hyperparathyroidism in children with chronic kidney disease [1]. The authors found that 77.2% of their patients with chronic kidney disease were vitamin D deficient/ insufficient, as defined by serum 25-hydroxycholecalciferol [25(OH)D3] levels of less than 30 ng/ml. Twenty-two of these patients received treatment with ergocalciferol, based on their serum 25(OH)D3 levels and in accordance with the guidelines of the Kidney Disease Outcomes Quality Initiative (KDOQI) [2]. Patients with vitamin D insufficiency [25(OH)D3 levels between 16 ng/ml and 30 ng/ml] were given ergocalciferol 2,000 IU daily for 12 weeks. Those who had 25(OH)D3 levels between 5 ng/ml and 15 ng/ml received ergocalciferol 4,000 IU daily for 12 weeks [2]. Parathyroid hormone (PTH) levels were noted to have fallen when checked 3 months after commencement of the ergocalciferol treatment.We have previously reported very similar findings in a study of 143 children with renal disease from our large tertiary referral centre in the north of the UK (latitude 53°26′) [3]. Of the children attending our outpatient clinics, 58% were vitamin D deficient/insufficient, defined as 25(OH)D3 levels of less than 20 ng/ml. A total of 83.2% had levels below 30 ng/ml, a value very similar to that reported in the study by Menon and colleagues, indicating the high prevalence of this problem on both sides of the Atlantic.It is well known that adherence to treatment is a major problem in children with kidney disease, particularly among adolescents [4]. Because there have been previous problems with significant non-adherence to prescribed therapy, we have recently changed our practice regarding the administration of ergocalciferol to vitamin D-deficient patients. We currently use a single large dose (100,000 IU for those 5-10 years of age and 150,000 IU for those over 10 years old), ingestion being witnessed in the outpatient clinic by the nephrologist or clinic nurse. The procedure is repeated every 3 months as necessary, according to 25 (OH)D3 levels. We have not used this regimen in children under 5 years of age, in whom adherence to treatment is less of a problem. Twenty children with very low levels of vitamin D [25(OH)D3 concentration of less than 16 ng/ml] were given a single dose of ergocalciferol. Their mean [standard deviation (SD)] age was 13.6± 3.4 years, with a range of 6-17 years. Baseline serum 25 (OH)D [25(OH)D2+25(OH)D3] levels were 1.5-15.8 ng/ ml [mean (SD) 8.1±3.4 ng/ml]. Three months after singledose treatment, measurement of the 25(OH)D levels was repeated and showed a significant rise to 7-25.6 ng/ml [mean (SD) 18.2±5.0 ng/ml, P<0.00001]. These results are presented in Fig. 1. The specific measurement of vitamin D2 concentrations, performed to determine the specific effect of the orally administered vitamin D2, showed an increase from 0 ng/ml (as none of our patients had been receiving vi...