Struggling and gasping for air, over 100 long-tailed macaques were rescued by Thai wildlife authorities after being stuffed in to carrier bags.
They were being illegally smuggled in the back of a pickup truck, more than a dozen did not survive.
The truck was intercepted at a checkpoint while on its way to a Thai province bordering Cambodia.
A field hospital was set up equipped with ultrasound scanners and breathing tubes, to treat 80 of the monkeys. Some were pregnant.
One of the vets said the animals were in a terrible state.
"The monkeys were exhausted and dehydrated for a long time. Some of them had respiratory problems because of overcrowding during the smuggling operation."
The driver of the truck is being detained for wildlife smuggling.
The man told local media that he was hired for $96 to drive the truck to the border and that he was not aware there were monkeys in the back of the vehicle.