Send JSON Data To HTTP Handler?

i have an ASP.NET 4.0 HTTP handler that should receive and send data in json format. I'm using jquery to send json objects serialized in a string to the handler. It correctly sends the request but i don't know how i could retrieve the data from the httpcontext passed to the handler and how i could deserialize it..

UPDATE 1

$.ajax({
type: "POST",
url: "myurl.ashx",
dataType: "json",
contentType: "application/json; charset=utf-8",
data: $.toJSON({
...
}),
success: function (response) {
...
}
});