An "AIDS kit", comprising a car calendar and fliers on testing and counselling tied neatly with a red ribbon, was distributed ahead of World AIDS Day on Saturday.
"The kit was attached to empty lunch boxes and delivered to about 100,000 clients' homes," said Raghunath Megde, leader of the lunch couriers, known as "dabbawallahs".
Some 5,000 dabbawallahs deliver 200,000 meals from their clients' homes all over Mumbai to their workplaces every day, a famous system studied in prestigious international business schools as a model of efficiency.
They collect lunch boxes from homes, sort them out using a system of colour codes and letters, travel by train and even carry massive wooden trays holding up to 35 tiffin boxes for delivery at offices.
Their error margin is said to be one in six million deliveries.
Megde says companies such as Mercedes-Benz, Microsoft and Coca-Cola have invited them to speak about their work.
Health groups sought the dabbawallahs' help for Friday's anti-AIDS campaign in order to be able to use their delivery mechanism.
India has the world's third biggest caseload of people living with the deadly virus. After originally estimating some 5.7 million were infected in India, the U.N. reduced that estimate to 2.5 million.
It says the global prevalence of HIV infections has levelled off, in part due to effective health programmes.