What is the antonym of nonchalantly?

Here are some antonyms of nonchalantly, depending on the specific context:

Strong Antonyms:

* Eagerly

* Enthusiastically

* Passionately

* Fervently

* With great care

* With great concern

Milder Antonyms:

* Carefully

* Attentively

* Seriously

* Seriously

* Concernedly

* With interest

The best antonym will depend on the specific situation and the nuances of the sentence you are using.