Thanks 22... you beat me to it! :-) It seems that in a nutshell, the stamps were like a semi-postal, with part of the cost supporting government run camps for kids.
The NZ post site says
Quote:
Health stamps
Health stamps are a distinctive New Zealand issue known by collectors around the world. The first ever Health stamp was issued on 11 December 1929 and featured the slogan 'Help Stamp out Tuberculosis'.
At the suggestion of the Health Department, it was decided that the Health stamps would carry a surcharge of 1d, which would be donated to the Children's Health Camps. These camps were started in Whanganui in 1919 to provide holiday health care for children with nutritional and minor physical problems.
Today, Health stamps still contribute to the seven Children's Health Camps around New Zealand, which aim to help children and families with complex needs to build healthy and happy lives.